Normally, I'd say you're wearing it...but for arenas, people are resilience whores and crits aren't quite so common because of that; with stacked ToWs you may still crit people(and if that's true, I'd keep the Chaotic), but if not, aim for the Haste rating meta to pop off more bolts + bonus to global cooldown. The name of said haste gem was mentioned in another thread, possibly the Ellay Advice one, by Fursphere, patch changed it from 50% cast time to haste rating

Edit: lol Fur beat me to it