Back again after some time to put some notes together on the Paladin.
The paladin is certainly one of the most powerful classes around, having both potent single target damage and incredible defences, and it works well with nearly every fighting style. You don't even need to invest strongly into damage feats like power attack, since Smite can easily prove to be just as valuable.
But, let's start from the beginning:
Recommended Ability Scores
Primarily, you're a martial character, so picking what you need for your fighting style is useful. Charisma is worth a good investment in as well, since it will impact lots of things, from uses of healing abilities to spells to enormous attack and defence boosts.
Basic stuff
You have full BAB (so you get to hit stuff), heavy armour and martial weapon proficiency. You've also got good fortitude and will saves. Skills and ranks are nothing at all to be excited about, so I'd suggest picking up a trait or two to rectify that. Additionally, you're required to be Lawful Good, and follow a Paladin Code.
Paladin Codes
It's worth bringing up the basic Paladin Code here. The basics of this are that you need to act honourably, respect legitimate authority, help those in need and punish those who would harm or threaten the innocent.
My personal view is that Paladins typically focus more on the being good aspect rather than the lawful aspect, so I have no issues with paladins who simply adhere to the more good aspect of it (and they can even be NG or CG).
It's also worth looking at the paladin codes of specific deities, which you use instead of the basic code. Some of these are much more satisfying than the basic one, and can very much change the whole nature of a paladin.
Smite Evil: Definitive Paladin ability. Find an evil thing and add your level to damage (or double that on first hit for some things), in addition to charisma to attack and AC. Also bypass all DR, which is incredible. Don't swap this with your archetype if you can avoid it.
Detect Evil: Something like this for free can be super useful, on so many levels, as a fairly generic Bad Guy locator.
Divine Grace: Get your charisma to all saves. So good, you'll never want to swap it out for anything.
Lay on Hands: Heal yourself a bit as a swift action. Excellent for not interfering with anything beyond smiting things, and makes you very difficult to kill. Don't swap this with your archetype if you can avoid it.
Aura of Courage: Immune to fear, and help friends be resistant as well. It's nice to have, but it's not a huge loss losing it, compared to the other features thus far.
Divine Health: Immune to diseases. Diseases I haven't found to be a substantial threat, so I wouldn't care too much about losing this.
Mercy: Remove a variety of conditions with Lay on Hands. You get a few of these over the levels, so it doesn't matter a whole lot if you lose any of these. Or all of them, since they aren't exactly fabulous.
Channel Positive Energy: Spend two Lay on Hands to heal everyone in a burst. If you have a big party, this is great, otherwise you can probably swap it out if your archetype lets you.
Spells: Merit its own section. Since you get this late, your caster level is often poor, so SR might be an issue. DCs aren't going to be high either, so consider mostly support spells.
Divine Bond: Either get a quite strong mount, or improve a weapon for a while each day. Depends on your purposes which you should pick, but the weapon's a decent option. It's not an enormous loss if this vanishes due to archetype.
Aura of Resolve: Immune to charm spells and help friends resist them. Will rarely see use unless you have intrigue based plots, so can definitely swap safely.
Aura of Justice: For two uses of Smite, your friends can also smite. If you have martial friends, this is incredible. Otherwise it's a load of junk that you should definitely swap.
Aura of Faith: Weapon is good aligned for overcoming DR, as it is for your friends. Kind of useless, since smite already beats this. Might be useful for your friends though? Worth swapping regardless.
Aura of Righteousness: Get DR 5/Evil and immunity to compulsions. Help friends resist compulsions. Going by a dumb rules as written approach, this makes you immune to beneficial spells such as heroism. Mostly useful otherwise, to be immune to the worst type of spell. The DR is almost redundant vs humans though by this stage.
Holy Champion: Capstone. DR increase to 10, Banish Evil Outsiders, and maximum heals on Lay on Hands. Reasonable capstone.
Archetypes
I'll use my normal system of Excellent, Good, Blah to rate these archetypes.
Chosen One: Lose divine bond for a familiar, and slightly delayed Smite and Divine Grace. Familiar does get to smite as well though, and can use lay on hands. It's a fairly reasonable trade.
Combat Healer Squire: Complete Garbage. Mundane healing and able to do it quickly to one specific person once per day, in exchange for detect evil, divine health and divine grace.
Divine Defender: Swap mercy for ability to boost nearby allies AC and saves using LoH. Divine bond is on Armour. Not a bad exchange at all.
Divine Hunter: Excellent ranged archetype, getting an excellent ranged feat in exchange for heavy armour, removing the awkwardness of cover from other friends and healing from a distance. Nothing much lost in the process.
Empyreal Knight: Lose divine grace for ability to speak celestial (and hard luck if you already could). Some nice passives in exchange for mercies. Lose Lay on Hands for rapid summon monsters. Divine bond is a mount. While your stuff is nice, the stuff you lose is too harsh to make this worth it.
Irorian Paladin: Pretend to be a monk. Charisma to AC, but lose good armour access. Detect things with ki instead of evil (useless). Smite evil becomes practically useless, except for being able to use it on non-evil things. Get better with rerolls and punching stuff in place of some useless things. All up not really worth it.
Holy Guide: Lose first two mercies for ranger favoured terrain and a teamwork feat that you can give to friends. Super good.
Holy Gun: Lose detect evil for gunsmithing and amateur gunslinger feat. Smite comes in a level late, and only functions on a single shot with a gun per round. Standard action, too, so no way around that. I guess you can potentially have an awful lot of smites though. While this is super cool for a Divine Sniper or something, if you really want guns, it's so much better to just take the one level dip in gunslinger.
Holy Tactician: An excellent choice for a large party. Smite isn't as strong, and doesn't last as long, but has the interesting effect of boosting your allies against things you attack, and it applies against all evil targets rather than just one. You lose divine health and bond as well as aura of courage in order to basically permanently give all your pals teamwork feats. Can even swap them as a swift action, because why not? Also lose Resolve in exchange for move action ability to let your friends move 5 feet for free. Kind of useless, but then, Resolve isn't that great either.
Redeemer: Half orc only. Easier to knock creatures out, lose detect evil for bonus to diplomacy vs 'monsters', and can force creatures to behave themselves in exchange for resolve. Don't actually lose much meaningful, so makes for a decent option.
Sacred Servant: The archetype if you want spells. Not so many smites, in exchange for a cleric domain, including bonus spells (!?). Divine bond becomes a kind of trashy flexible boost to LoH/channel/Caster level. Resolve turns into a very nifty once per week free planar ally spell. If it weren't for divine bond being so poor, I'd say this'd be an excellent default.
Sacred Shield: Smite instead halves the damage target does against you and nearby allies. Can spend LoH to give nearby friends a shield bonus to AC. Divine Bond applies to your shield, and capstone gives you and friends regeneration vs the target of your smite. This is... interesting. Not remarkable, but interesting.
Shining Knight: The way to go if you're mounted. Basically alters stuff to also boost your mount and make you better on a mount.
Stonelord: Dwarf only. Get different and fairly decent defence changes, but reduce smite to point of uselessness, and lose spells. Junk.
Sword of Valour: Lose divine grace for being better in surprise rounds and initiative bonus. A mercy becomes mass temp hp. Justice becomes chance for enemy to surrender if smitten and crit. The mercy is about the only worthwhile trade here.
Temple Champion: Lose spells for a domain, and divine bond and justice for warpriest blessings. Utter garbage.
Tranquil Guardian: Aasimar only. Smite becomes touch of serenity (target saves or can't use spells or attack for 1 round). Immune to emotion instead of charm, can use touch of serenity on a crit, and can make a tiny AoE with touch of serenity. Useless.
Undead Scourge: Extra good vs undead for little penalty. Campaign dependant, not recommended otherwise.
Warrior of the Holy Light: Lose spells in exchange for a few extra LoH and can use to to give minor buffs. Faith becomes an awesome high DC damage + heal ability a few times a day. The latter is super good, the former is dreadful. Skip.
Alternate Paladin Oaths
These are add-ons to the standard vows, and can function a little like archetypes. You often get extra spells on your list with these.
Oath vs. Chaos: Basically standard paladin, but vs chaos instead of evil. Channel instead lets you use a LoH and smite to hit evil instead of chaos. Usually not worth it.
Oath vs Corruption: Be good vs Aberrations (as well as evil). Campaign dependant.
Oath vs fiends: Stop evil outsiders teleporting near you in exchange for resolve, and swap a mercy for ability to boost armour and shield with resolve. Even if it's campaign dependant, you're not losing much for a potential decent boost.
Oath vs Grotesquery: Be pretty good vs transmutations and can restore charisma damage in exchange for divine health and faith. Well worth it (since this hits nasty things like disintegrate)
Oath vs Savagery: Lose divine grace for potential reach boost. Justice for more AoOs and slightly more damage on them. Loss of divine grace makes this a poor option.
Oath vs undeath: Unsurprisingly, this makes you good vs undead and ghosts. Since you swap detect evil for detect undead, pick only if necessary for campaign.
Oath vs the wyrm: Be good vs dragons. Possibly worth it for the spells, but otherwise only if your campaign suggests it.
Oath of Charity: Heal others more but yourself less with LoH, and can swap mercies around easily in place of divine bond. Pick if your character demands it.
Oath of Chastity: Divine grace only on Will saves, but resolve becomes 50% crit/sneak immunity. Worth considering.
Oath of loyalty: Smite goes, instead letting you boost a friend's AC for a short while. Junk.
Oath of Vengeance: Lose channel for possibility of lots of extra smites. Good spells, too. A good default.
Best Spells
Loads of spells here, so I'm only going to pick out the cream of the crop. DCs are going to be low, so keep this in mind for combat spells.
1st level spells
Bless Weapon: Auto Confirm crits.
Cure light wounds: Small heal, but there's not much else remarkable here.
Hero's Defiance: Use Lay on Hands as immediate action if you fall unconscious, plus an extra 1d6.
Honeyed Tongue: Reroll and take highest on diplomacy checks.
Knight's Calling: Force a creature to spend it's turn moving to you, and you get to hit it if it reaches you.
Veil of Positive Energy: +2 sacred bonus to AC and saves vs undead, for actually quite a while.
2nd level spells
Bestow Grace: Give good target bonus on saves equal to its charisma bonus
Ironskin: Huge natural armour bonus
Litany of Righteousness: Swift action to cause a creature to take double damage from creatures with a good aura for a round.
Resist Energy: Take reduced damage from energy damage.
Widen Auras: Some archetypes might find that doubling their aura size is useful.
3rd level spells
Angelic Aspect: Get DR 5/evil, darkvision, acid/cold resistance and fly speed.
Magic Circle vs Chaos/Evil: Long lasting group protection from nasty effects.
Greater Magic Weapon: Long lasting attack and damage boost, if you haven't got a good weapon yet
Sanctify armour: as above, but for armour.
Tail Strike: Grow a tail that you can use as a secondary attack. More attacks is always good!
4th level spells
Greater Angelic Aspect: Okay, now this is ridiculous. Immunity to cold and acid, fire and electricity resist 10, Darkvision, DR 10/evil, Truespeech, 60 ft. fly speed, +4 deflection and resistance vs evil things in an aura, as well as a lesser globe of invulnerability.
Bloodsworn Retribution: An interesting spell, reduce max hp while you fulfill an oath in order to gain bonus on everything related to that oath.
Eaglesoul: Long lasting spell that kind of lie dormant until you activate it, at which point it gives you auto confirmed crits, Str and AC boosts and fast healing.
Well, hope that's useful for someone besides me. It's good for me to do them, if nothing else, so I can look back on these notes and quickly pick a good archetype.
The paladin is certainly one of the most powerful classes around, having both potent single target damage and incredible defences, and it works well with nearly every fighting style. You don't even need to invest strongly into damage feats like power attack, since Smite can easily prove to be just as valuable.
But, let's start from the beginning:
Recommended Ability Scores
Primarily, you're a martial character, so picking what you need for your fighting style is useful. Charisma is worth a good investment in as well, since it will impact lots of things, from uses of healing abilities to spells to enormous attack and defence boosts.
Basic stuff
You have full BAB (so you get to hit stuff), heavy armour and martial weapon proficiency. You've also got good fortitude and will saves. Skills and ranks are nothing at all to be excited about, so I'd suggest picking up a trait or two to rectify that. Additionally, you're required to be Lawful Good, and follow a Paladin Code.
Paladin Codes
It's worth bringing up the basic Paladin Code here. The basics of this are that you need to act honourably, respect legitimate authority, help those in need and punish those who would harm or threaten the innocent.
My personal view is that Paladins typically focus more on the being good aspect rather than the lawful aspect, so I have no issues with paladins who simply adhere to the more good aspect of it (and they can even be NG or CG).
It's also worth looking at the paladin codes of specific deities, which you use instead of the basic code. Some of these are much more satisfying than the basic one, and can very much change the whole nature of a paladin.
Smite Evil: Definitive Paladin ability. Find an evil thing and add your level to damage (or double that on first hit for some things), in addition to charisma to attack and AC. Also bypass all DR, which is incredible. Don't swap this with your archetype if you can avoid it.
Detect Evil: Something like this for free can be super useful, on so many levels, as a fairly generic Bad Guy locator.
Divine Grace: Get your charisma to all saves. So good, you'll never want to swap it out for anything.
Lay on Hands: Heal yourself a bit as a swift action. Excellent for not interfering with anything beyond smiting things, and makes you very difficult to kill. Don't swap this with your archetype if you can avoid it.
Aura of Courage: Immune to fear, and help friends be resistant as well. It's nice to have, but it's not a huge loss losing it, compared to the other features thus far.
Divine Health: Immune to diseases. Diseases I haven't found to be a substantial threat, so I wouldn't care too much about losing this.
Mercy: Remove a variety of conditions with Lay on Hands. You get a few of these over the levels, so it doesn't matter a whole lot if you lose any of these. Or all of them, since they aren't exactly fabulous.
Channel Positive Energy: Spend two Lay on Hands to heal everyone in a burst. If you have a big party, this is great, otherwise you can probably swap it out if your archetype lets you.
Spells: Merit its own section. Since you get this late, your caster level is often poor, so SR might be an issue. DCs aren't going to be high either, so consider mostly support spells.
Divine Bond: Either get a quite strong mount, or improve a weapon for a while each day. Depends on your purposes which you should pick, but the weapon's a decent option. It's not an enormous loss if this vanishes due to archetype.
Aura of Resolve: Immune to charm spells and help friends resist them. Will rarely see use unless you have intrigue based plots, so can definitely swap safely.
Aura of Justice: For two uses of Smite, your friends can also smite. If you have martial friends, this is incredible. Otherwise it's a load of junk that you should definitely swap.
Aura of Faith: Weapon is good aligned for overcoming DR, as it is for your friends. Kind of useless, since smite already beats this. Might be useful for your friends though? Worth swapping regardless.
Aura of Righteousness: Get DR 5/Evil and immunity to compulsions. Help friends resist compulsions. Going by a dumb rules as written approach, this makes you immune to beneficial spells such as heroism. Mostly useful otherwise, to be immune to the worst type of spell. The DR is almost redundant vs humans though by this stage.
Holy Champion: Capstone. DR increase to 10, Banish Evil Outsiders, and maximum heals on Lay on Hands. Reasonable capstone.
Archetypes
I'll use my normal system of Excellent, Good, Blah to rate these archetypes.
Chosen One: Lose divine bond for a familiar, and slightly delayed Smite and Divine Grace. Familiar does get to smite as well though, and can use lay on hands. It's a fairly reasonable trade.
Combat Healer Squire: Complete Garbage. Mundane healing and able to do it quickly to one specific person once per day, in exchange for detect evil, divine health and divine grace.
Divine Defender: Swap mercy for ability to boost nearby allies AC and saves using LoH. Divine bond is on Armour. Not a bad exchange at all.
Divine Hunter: Excellent ranged archetype, getting an excellent ranged feat in exchange for heavy armour, removing the awkwardness of cover from other friends and healing from a distance. Nothing much lost in the process.
Empyreal Knight: Lose divine grace for ability to speak celestial (and hard luck if you already could). Some nice passives in exchange for mercies. Lose Lay on Hands for rapid summon monsters. Divine bond is a mount. While your stuff is nice, the stuff you lose is too harsh to make this worth it.
Irorian Paladin: Pretend to be a monk. Charisma to AC, but lose good armour access. Detect things with ki instead of evil (useless). Smite evil becomes practically useless, except for being able to use it on non-evil things. Get better with rerolls and punching stuff in place of some useless things. All up not really worth it.
Holy Guide: Lose first two mercies for ranger favoured terrain and a teamwork feat that you can give to friends. Super good.
Holy Gun: Lose detect evil for gunsmithing and amateur gunslinger feat. Smite comes in a level late, and only functions on a single shot with a gun per round. Standard action, too, so no way around that. I guess you can potentially have an awful lot of smites though. While this is super cool for a Divine Sniper or something, if you really want guns, it's so much better to just take the one level dip in gunslinger.
Holy Tactician: An excellent choice for a large party. Smite isn't as strong, and doesn't last as long, but has the interesting effect of boosting your allies against things you attack, and it applies against all evil targets rather than just one. You lose divine health and bond as well as aura of courage in order to basically permanently give all your pals teamwork feats. Can even swap them as a swift action, because why not? Also lose Resolve in exchange for move action ability to let your friends move 5 feet for free. Kind of useless, but then, Resolve isn't that great either.
Redeemer: Half orc only. Easier to knock creatures out, lose detect evil for bonus to diplomacy vs 'monsters', and can force creatures to behave themselves in exchange for resolve. Don't actually lose much meaningful, so makes for a decent option.
Sacred Servant: The archetype if you want spells. Not so many smites, in exchange for a cleric domain, including bonus spells (!?). Divine bond becomes a kind of trashy flexible boost to LoH/channel/Caster level. Resolve turns into a very nifty once per week free planar ally spell. If it weren't for divine bond being so poor, I'd say this'd be an excellent default.
Sacred Shield: Smite instead halves the damage target does against you and nearby allies. Can spend LoH to give nearby friends a shield bonus to AC. Divine Bond applies to your shield, and capstone gives you and friends regeneration vs the target of your smite. This is... interesting. Not remarkable, but interesting.
Shining Knight: The way to go if you're mounted. Basically alters stuff to also boost your mount and make you better on a mount.
Stonelord: Dwarf only. Get different and fairly decent defence changes, but reduce smite to point of uselessness, and lose spells. Junk.
Sword of Valour: Lose divine grace for being better in surprise rounds and initiative bonus. A mercy becomes mass temp hp. Justice becomes chance for enemy to surrender if smitten and crit. The mercy is about the only worthwhile trade here.
Temple Champion: Lose spells for a domain, and divine bond and justice for warpriest blessings. Utter garbage.
Tranquil Guardian: Aasimar only. Smite becomes touch of serenity (target saves or can't use spells or attack for 1 round). Immune to emotion instead of charm, can use touch of serenity on a crit, and can make a tiny AoE with touch of serenity. Useless.
Undead Scourge: Extra good vs undead for little penalty. Campaign dependant, not recommended otherwise.
Warrior of the Holy Light: Lose spells in exchange for a few extra LoH and can use to to give minor buffs. Faith becomes an awesome high DC damage + heal ability a few times a day. The latter is super good, the former is dreadful. Skip.
Alternate Paladin Oaths
These are add-ons to the standard vows, and can function a little like archetypes. You often get extra spells on your list with these.
Oath vs. Chaos: Basically standard paladin, but vs chaos instead of evil. Channel instead lets you use a LoH and smite to hit evil instead of chaos. Usually not worth it.
Oath vs Corruption: Be good vs Aberrations (as well as evil). Campaign dependant.
Oath vs fiends: Stop evil outsiders teleporting near you in exchange for resolve, and swap a mercy for ability to boost armour and shield with resolve. Even if it's campaign dependant, you're not losing much for a potential decent boost.
Oath vs Grotesquery: Be pretty good vs transmutations and can restore charisma damage in exchange for divine health and faith. Well worth it (since this hits nasty things like disintegrate)
Oath vs Savagery: Lose divine grace for potential reach boost. Justice for more AoOs and slightly more damage on them. Loss of divine grace makes this a poor option.
Oath vs undeath: Unsurprisingly, this makes you good vs undead and ghosts. Since you swap detect evil for detect undead, pick only if necessary for campaign.
Oath vs the wyrm: Be good vs dragons. Possibly worth it for the spells, but otherwise only if your campaign suggests it.
Oath of Charity: Heal others more but yourself less with LoH, and can swap mercies around easily in place of divine bond. Pick if your character demands it.
Oath of Chastity: Divine grace only on Will saves, but resolve becomes 50% crit/sneak immunity. Worth considering.
Oath of loyalty: Smite goes, instead letting you boost a friend's AC for a short while. Junk.
Oath of Vengeance: Lose channel for possibility of lots of extra smites. Good spells, too. A good default.
Best Spells
Loads of spells here, so I'm only going to pick out the cream of the crop. DCs are going to be low, so keep this in mind for combat spells.
1st level spells
Bless Weapon: Auto Confirm crits.
Cure light wounds: Small heal, but there's not much else remarkable here.
Hero's Defiance: Use Lay on Hands as immediate action if you fall unconscious, plus an extra 1d6.
Honeyed Tongue: Reroll and take highest on diplomacy checks.
Knight's Calling: Force a creature to spend it's turn moving to you, and you get to hit it if it reaches you.
Veil of Positive Energy: +2 sacred bonus to AC and saves vs undead, for actually quite a while.
2nd level spells
Bestow Grace: Give good target bonus on saves equal to its charisma bonus
Ironskin: Huge natural armour bonus
Litany of Righteousness: Swift action to cause a creature to take double damage from creatures with a good aura for a round.
Resist Energy: Take reduced damage from energy damage.
Widen Auras: Some archetypes might find that doubling their aura size is useful.
3rd level spells
Angelic Aspect: Get DR 5/evil, darkvision, acid/cold resistance and fly speed.
Magic Circle vs Chaos/Evil: Long lasting group protection from nasty effects.
Greater Magic Weapon: Long lasting attack and damage boost, if you haven't got a good weapon yet
Sanctify armour: as above, but for armour.
Tail Strike: Grow a tail that you can use as a secondary attack. More attacks is always good!
4th level spells
Greater Angelic Aspect: Okay, now this is ridiculous. Immunity to cold and acid, fire and electricity resist 10, Darkvision, DR 10/evil, Truespeech, 60 ft. fly speed, +4 deflection and resistance vs evil things in an aura, as well as a lesser globe of invulnerability.
Bloodsworn Retribution: An interesting spell, reduce max hp while you fulfill an oath in order to gain bonus on everything related to that oath.
Eaglesoul: Long lasting spell that kind of lie dormant until you activate it, at which point it gives you auto confirmed crits, Str and AC boosts and fast healing.
Well, hope that's useful for someone besides me. It's good for me to do them, if nothing else, so I can look back on these notes and quickly pick a good archetype.