Fun to Level - Warlock
Effectiv in Raids - Shaman
Fun to Play - Mage
Helpful in Dungeon and Raids - Priest
Shaman is allways welcome in raids etc Hero/ Bloodlust ftw, mages have thousands of possabilitys to get played.
Priests are well known healers ^^ and can be leveld easy aswell (insane mana reg + dot dot dot!!!!)
The Warlock does massiv dmg in raids, fun at PvP and is freakn awesome to level, you just run around and spam dots on everything on sight :P
Well... at the end you have to know what you want to play!