Since you'll be using KA all three tanks work rather well. There are some differences to them, but here is my experience in comparison.
Warrior - Hands down the easiest for a cleric/merc to heal. Also the 'best' at handling multiple mobs. If you are personally slow to lock down mobs, the warrior is going to do much better at letting 2 or 3 mobs beat on him than either of the knight classes. That is not to say that they are not good tanks, but a warrior mitigates better and just has a smoother spike curve over all. Also, the easiest to do named with while still getting gear. Once you are fully geared for the expansion this becomes less relevant as the knights begin to 'catch up'.
Paladin - Very powerful self heals, so much so that once his gear catches up to the current content he often won't even need a cleric merc, and can just heal himself while tanking. It's a bit riskier but often when we go back into content like CoTF HAs our paladin will just pull out another DPS merc and we'll rip through the mobs. Has the ability to also splash heal, cure, etc. Very handy for those fights with heavy AEs or needs for cures. I'd also challenge that paladins probably have the BEST single target aggro, so if there is only one mob in camp you can have all your wiz mercs/wizard/etc on full burn and he will have a much easier time holding aggro than the other two (though warrior is close, and sk's are no chumps either.)
SK - Sks are very sturdy tanks but their lifetaps don't seem to have caught up with the self healing of a paladin. They are still quite nice, but not quite where they need to be. The instant terrors are very handy for making sure they get aggro earlier than the paladin (snap aggro), but the true beauty of an sk is his ability to aggro everything with AE terrors. If you have 8 mobs in camp mezzed, odds are the SK is going to have aggro on all of them set before he even finishes killing the first one. I find the sk is harder to keep alive than the other two in current content, but his DPS is higher and his utility as a backup puller/kiter etc well make up for that.
I currently use a paladin, but I have a warrior and sk and sometimes use them as well. (The paladin was the first to 105 though and haven't even bothered with the other two. Still dunno that I'll bother with buying TDS for that account. )