The original Vex, by far. I received my Vex after they nerfed it, but man I got my ass handed to me when it was dominating PvP. Necrochasm was a severe fail - all the hype and the grind for the crux for a mediocre pellet gun. The buff they gave it should have happened in the same time frame that they nerfed the Vex, not a week before it was going to become a mere trophy.