I don't usually chime in on this board, but I do feel compelled to add something to the ongoing discussion around paladins, as it is one of my favorite classes hands down. I'll try to write something legible, but I can't make any promises.
I personally believe the paladin class, as it is now, should be rebuilt from the ground up. The current iteration of the class locks us into a singular role (that of the party defender), but fails to provide the necessary tools to fill out that role.
The paladin has few to no true offensive options available (smite being locked on a reaction comes to mind), and the defensive options depend highly on the generosity or foolhardiness of your GM. While thematically nice, retributive strike can more often than not be easily circumvented by enemy NPCs, and it is ridiculous to assume, that all campaigns will take part in a 3x3 rooms or corridors, just so that the paladin gets the possibility to shine.
I find most of the available champion powers to be lackluster at best. There are too few, with half level they don't scale that well, and frankly you don't get to have too many spell points to spend if you don't exclusively focus on charisma. Which ties into another gripe. I don't really see, how charisma actually benefits this martial class in this version of pathfinder. It gives you spell points, which is nice but can be substituted by multi-classing (Cleradin) and it boosts our smite. Which is tied to a reaction.
Permanent damage is powerful, but just to boost charisma to be able to douse demons in holy acid. Kind of a one trick pony.
I would propose that the class should be structured similarly to the druid or bard, as in that we need to choose the major theme at the start. Class feats associated with that theme get boosted, giving you an incentive to stay with that role. Call them orders or oaths, or something thematically appropriate. With this we can open up the possibilities, where the paladin can go and give more class and role playing opportunities to the player, instead of a singular role.
For example
Oath of the Crusader
Theme: "The crusader seeks out evil, where ever it may hide and roots it out with extreme force. There can be no mercy for those that pray on the innocent."
The crusader is a "proactive" defender. They gain a number of offensive options, while forgoing some of the defensive options a paladin normally gets. This could go along the line of increasing weapon proficiency for either a single weapon group or deific weapons at the cost of lower proficiency in heavy armor.
Add a holy smite action to the paladins arsenal.
General (all paladins): Use 1 spell point / champion power. Make a strike against a (visible, targetable) enemy within range. Add your charisma modifier (min 0) to your attack and damage roll. This bonus damage is good/holy damage.
Oath specific: the crusader turns all damage to good/holy.
Holy smite gains additional damage dice and debuff options further down the line. Also a two action version with charge (so two strides and a strike)
Crusaders must take the weapon ally.
A crusader adds the following line to the paladin code of conduct:"You may never back down from a challenge against a truly evil foe."
Oath of the Defender
Theme: "The defender holds the line against the enemies of his faith. They are the rock against wave after wave of enemies shatter themselves".
The defender keeps most of the same mechanics and themes of the current iteration the same. They focus on protecting the party and themselves with, thus becoming the groups prime tank.
Retributive strikes gets the following changes.
General (all oaths): Add a stride action to retributive strike. If a friendly or allied creature is attacked you may take a stride action to move up to your speed and intercept. You take attacks of opportunity as normal. If you can't get in range to strike the enemy you can't take this action.
Oath specific: While wielding your deities favorite weapon you may add reach to the weapon properties, when making a retributive strike.
Retributive strike can later be upgraded to use a step action (same range) instead of a stride action, you may gain additional uses per round, you can add more and nastier debuffs or you can use it on yourself as well.
Defenders must take the shield ally. They gain the divine grace feat, which grants static bonuses (instead of a reaction).
A defender adds the following line to the paladin code of conduct: "You may never abandon a party member as long as there is a chance to save them".
Oath of Heroism (Champion Powers, Leadership)
I was thinking of questing knights, healing the sick, rallying the local populace to overthrow tyranny and generally being the party face. Less martially inclined (or at least less hands on) as the other two variants.
The heroic paladin could focus on buffing his allies with auras and some better champion powers. Additionally they get the mount. This one I'd need to think through some more, but I liked the idea of the paladin being the shiny beacon of hope.
Going in this direction we open up so many possibilities to play the class as people would like. And with this I ran out of steam and ideas. I may edit this later for form, grammar and spelling, but I do hope my point (if any) came across.