Well at the moment Warriors, BM Hunters, and Mages ( no surprise there) are at the top overall. Resto druids seem to be one of the top healers at the moment. Can't say specifically which are better for RBGS.
Roll whichever class you're best at playing -- pretty much every class gets their shine in the spotlight with the way Blizzard constantly nerfs/buffs classes in cyclical fashion, so eventually yours will be there too.
PvP is a complete travesty right now, I've completely stopped playing WoW because of it. Monstrous burst that drops you in seconds and CC that controls you more than you can actually play. Almost as bad as S5.