arms is stupid good right now from what I've seen in arenas, but this is at max level. I've heard they're good for twinking, but do note that the further we get along in the expansion and the more that people hit higher ilvls it gets harder to hold our own in wpvp, especially since we have a chance of missing our attacks (and some are crucial to our dps).
If you want to gank levelers then yeah arms is deff a good choice, but you might have some issues going against some max level player with >3m hp. I find that on my hunter and boomie i can somewhat get someone at max level if they're less than 3m hp.