Derrick Williams? He is a great dunker no doubt, but he is more of an in game/power dunker.
Evans dunks in practice aren't anything special anyway. Jumping over a player? Really? That's the dunk you're expecting to get you into the dunk contest? Nobody outside of Utah fans knows who Evans is anyway. Besides, the NBA has changed the way they judge the dunk contest this year. It's all a fan vote. No more judges holding up cards. Each dunker gets 3 dunks and then the fans vote via text, twitter who wins the contest.