I think anything with combo points sux.
druid boomkins & druid cats are a no while druid tanks are fine.
but as far as I've played them
tanks:
pally 10
bear 9
haven't tried the rest.

ranged
ele-shaman 10
ice-mage 10 ( so simple it hurts and the team almost never runs out of mana )
hunters 9
warlocks 9
arc-mage 9
boomkin 7-8 ( eclipse sux until you get some really high crit rating, multiple booms can't all eclipse at the sametime )

melee:
ret-pally 10

healers:
shaman 10
priest 9/10
druid 9
pally 7 <<, no real aoe panic heals, too much micro management for my taste, they are very good single target healers but for boxing the shaman chain heal rules.


as far as I'm concerned my strongest teams are
pally, 3 ele-sham, rest-sham 10
pally, 2 ele-sham, frost-mage, rest-sham 10
pally, 3 ret pally, rest -sham 10
bear, 3 locks, priest 9/10
5 pally, prot, 3x ret, 1 holy 8 << ok until you need a lot of heals