Well, I'll give you my 2c based on my experience. I have 4x Shamans, 4x DKs and 4x Druids at 80.

I LOVE the shamans, nuff said.

I LOVE the DKs, they are so much fun and a good break from the one button wonder shamans. You need to actually work to kill people conserve your cooldowns and if played correctly you can destroy far more people in a row than shamans (due to no loss of mana, ever)
I HATE my druids.. Now, I haven't bothered to gear them up significantly because they are just painful right now. Boring as heck and honestly not as good as shamans while trying to do the same thing. They MAY be better as 4x resto or 4x feral, but 4x Moonkin is just.. not doing it for me.

I have 4x Paladins in the early 70's and so far they are pretty fun. I am not sure they will be as good as DKs at 80 yet, I am still lvling them and decising, but so far they dont seem to have as good of synergy as the DKs (cooldowns leave Paladins sitting with their balls in the wind for a few seconds no matter what)

4x Hunters, Warlocks, priests at 70 and not interested in lvling them atm. They all seem not defensive enough to compete in BGs legitimatly.