My main is a warrior and I've become very frustrated with tanking heroics (my gear isn't top notch yet and I'm not in a large guild). So I've moved to the PvP area.
With that said, I don't have that much arena experience, mostly because I've been farming the honor gear so that I can hold my own in arenas (instead of just getting massacred).
My main PvP spec right now is Arms tbh. However, I do have a Prot spec that is viable in Heroic tanking AND in BGs. Prot in PvP is mildly frustrating:
1) your mobility is not that great compared to Fury or Arms (usually)
2) Burst damage is lower. Your biggest burst dmg is usually going to come in the form of a concussive blow, followed up by a Shield Slam (Shield Block).
However, it is quite fun, as mages and those pesky casters that try and kite you just don't know what hit them when you perma-stun them with charge -> concussive blow -> shockwave -> shield bash.
Also, if you're doing BGs then you know that a tank is required for AV and Isle of Conquest so.... its always nice to have your tank set and your PvP set and swap between them when you have a boss to tank.
Just my 2cents. (In all honesty though Arms and Fury are probably the way to go if you're serious about Arena PvP).