I've been pugging quite a bit as a healer lately (+10/+11) and there seem to be two types of tanks, independend from the class: those that need healing, and those that don't*.
* exaggeration, of course. But I'm sure every other healer knows what I'm meaning.
Generally when I am healing (Mistweaver) I prefer Tanks that mitigate damage over self-healing Tanks.
It is simply easier to work with. Their health is low = heal. You don`t have to worry about ruining and wasting their self-heal or wasting your own mana by starting a cast and in the same second their health shoots up again.
So I`d say Brewmaster is my favourite since you can mostly keep them alive by keeping Hots ticking on them (basically healing a Brewmaster is like healing a target with moderate to heavy DoT ticking constantly so ticking heals are nice to counteract that kind of damage)
Warrior is a close second (and usually what I have to work with ) still very smooth damage intake, not usually spiky unless they forget their Shield Block.
Pala is bit middle of the ground, fine too, very sturdy, but if they waste their charges it will look more ugly. Also you are bound to waste either your own heals or the Pala`s selfheal at some points.
VDH and DK give me heartattacks... I try not to have heartattacks.
Druids... have a Tank spec? Haven`t seen one for month.