warlocks can smoke most pre-bc dungeons, they won't be quite as awsome after level 60 but they are still awsome.
Hunters are just fun but you might want a healer on the team.
pally's are awsome at least thru level 70 ( there is no dungeon they can't do ) with ony a few dungeons giving them any trouble in WoLK ( I had trouble with UK last boss, Azjol-Nerub 2nd&3rd bosses , HoL 3rd boss is giving me hell )