I've tried Xgl and Aero glass, and I'd have to say I like aero glass better. It runs fine on my system. It looks better, and I don't think the features of Xgl are that great...it looks boring to me. And the jellow windows are fun for a bit, but I got tired of them.
Sticking to aero (which I'm sure will be a lot better, at least optimized, in the future).