I prefer Dan, much because I feel like he pushes himself more, and not just in terms of just range. If you really study the way Dan sings it's incredibly diverse. He tries different styles, small nuances that you don't even always hear that makes his vocals more interesting than Ashe's. Ashe just sort of has his one thing he does, and he does it great, but it's not as rich.
Not saying that Ashe is bad though, I think his voice is lovely, but Dan is one of my biggest idols in music.