I play Merc quite a bit and have recently switched to an alacrity build. I am rocking 104.99% accuracy, 37% crit, 68% surge, and a little over 10% alacrity. Seems like the big hits are about the same, but the overall damage is quite a bit more. I really think it's personal preference when gearing out toons, but I would try that build. Alacrity is pretty over looked right now I feel like.