It still seems weird, by design, that there are lots of goodies in the Defender tree, but as you're going to want some DPS from the Knight tree, you are left needing to pick and choose which of the goodies in the Defender tree to go with, but whatever. It is what it is, and I don't really mind.
To the OP, and everyone else out there, IMHO below are the base set of enhancements to take from the Knight and Defender tree. This is based on my play-testing to date, as well as my experience in playing Paladin tanks for over 7 years now. These represent the minimum I would spend in each tree.
Knight Tree
-Slayer of Evil I and II - 2 APs - Core
-Courage of Heave & Improved Courage of Heaven - 2 APs - Core
-Extra Turns - 2 APs - level 1 (this is just for prereq for level 2, any other 2 APs would work at level 1)
-Extra Smites - 2 APs - level 1
-Extra Smites - 2 APs - level 2
-Divine Might - 6 APs - level 2
-Exhalted Smite - 6 APs - level 3
-Divine Sacrifice - 3 APs - level 3
-Vigor of Life - 2 APs - level 3
-Vigor of Life - 2 APs - level 4
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29 APs
Defender Tree
-Holy Bastion through Glorious Stand - 5 APs - Core
-Extra Lay on Hands - 3 APs - level 1
-Improved Sacred Defense / PRR - 3 APs - level 1
-Bulwark Aura / Sacred Armor Mastery (at low levels, Bulwark Aura will be better, but once you get a good dodge item and/or you can fill out the max dex. bonus at higher levels, switch to Sacred Armor Mastery) - 3 APs - level 2 or 1
-Improved Sacred Defense / Hate - 3 APs - level 2
-Improved Sacred Defense / Saves - 3 APs - level 3
-Greater Sacred Defense / Strength - 3 APs - level 3
-Greater Sacred Defense / Hit Points - 3 APs - level 4 (Note: this is bugged at the moment and you will temporarily lose the bonus hit points when you swap weapons, even with a shield equipped)
-Swift Defense - 1 AP - level 4
-Reinforced Defense / Armor - 6 APs - level 4
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33 APs
So in total, that's 62 total APs, leaving 18 more to spend in a different class or racial tree, or more in the defender or knight tree. There are a lot of other good choices. Personally, I am leaning away from the aura enhancements (Bulwark, Resistance and Spellshield) because 1) a Paladin's aura is primarily for the benefit of the Paladin, and 2) I think you get a better bang for your buck/AP elsewhere, such as tier 5 defender stuff, or perhaps more in the Knight tree. Also, if you're going to use a tower shield you'll want Sacred Shield Mastery maxed. I just don't see having room for the aura enhancements, unless based on Lorianna's feedback, you go Drow and max out spell resistance, which sounds like an intriguing idea
In any event, I hope this helps.