I agree with Zal

Pally = 1 button tank. Also this dude has a ton of buffs.
Dk = I usually use 3 buttons. (3rd for DnD) This guy has 3 OHH shit buttons as Multibocks stated.
Warrior i have not been using in Wotlk more then when i raid with the guild. in my opinion this is the best singel target tank.
Druid, i have no XP using a druid, only what i have read so ill leave this for now.. in 3.1 they get some changes so it might not be a bad choise though.

It really comes down to what you want to play.