EI am going to stay prot for arena season 5 for several reasons (assuming I still have my uber ret pally partner).
1) He does enough damage, and with all of the support abilities I will have as a prot warrior, he should be able to smash them into the ground. Some of the abilities that I really like for PvP
a) Gag Order: If you are specced into this, you really are a caster's worst nightmare. You can silence them from a distance with heroic throw, or while you are up close with a good ole shield bash.
b) Warbringer: Charging in combat from any stance is hawt. Having it break snare effect such as frost nova is extra hawt. A warbring charge followed by a sheld bash is BAAAAAADDDDD for casters.
c) Concussion Blow: Not only does it stun the opponent, but it hits for a very good amount of damage. Mine crits for over 3k.
d) Shield Slam: Besided being a prot warrior's big damage ability, it also takes a buff off of the target. Get a few of these in and you opponent will be practically naked.
e) Shockwave: A nice chunk of damage and an even better AOE stun.
f) Improved Spell Reflect: It will be more deadly for casters to focus fire now. Improved spell reflect not only reflects for you, but you teammate. Frostfire bolt in your FACE.
g) Damage Shield: Watch and laugh as a rogue beats himself to death.
h) Other nice abilities for warriors: Enraged regenration is a nice self heal, and intimidating shout is a nice interrupt. Lets not forget that retalliation and shield wall are now on seperate 5 minute cooldowns and shield block will come in handy against rogues.
It aint bad to be prot in PvP anymore.