The short answer is it depends on what other classes you're playing with and what type of PvP you're doing. For example Shaman are good arena healers, and a Blood DK has ridiculous amounts of survivability. Rogues always have a place as an annoying ambusher in BGs at minimum.
Basically pick whatever class you enjoy playing. I enjoy my rogue (and I've tried to switch mains before), so I play my rogue even when rogues aren't the most powerful class.
I only really do PvE, but find Retadins to be annoyingly clunky at the moment and have pretty much given up on playing my pally. Can't speak for tanking or healing though. I'm levelling a combat rogue at the moment (currently level 82) and it's more fun than ret.