For me, the choice was simple. All the videos and reviews I saw while I was researching a new phone convinced me that I wanted HTC (and the Sense UI), and I'm on AT&T. So, it was Aria all the way.
So far, I've been very happy. It would be cool if I could turn Sense on and off, though, just so I could see how the "other half" lives. And, it will be cool to be able to sideload apps when I decide to root my device. That'll be after I get tired of Sense (or at least, more familiar with it) and I get adventurous enough. l can wait a while before exploring that territory. For right now, the quantum leap from my old Nokia (Symbian OS) has been big enough to keep me occupied!