Hybrids are beasts, high damage, high healing. Especially priests (disc). Warriors and Rogues are great aswell. If you just want carnage at the lowest brackets then I'd recommend either priest or rogue. Retribution paladins were (before MoP, not sure now though) AMAZING at the level 30+ brackets!
Resto druids are virtually impossible to kill. Mana regen is too good, and mana costs are FAR too low... it's like 7mana for rejuv at level 20+..laughable.
Spam rejuv, shapeshift out of shit, switch to cat form and kill people as if you specced feral because it still hits hard... /lol at everyone.