I had to play around with a OneX in store to judge if I wanted an Evo because no stores in town have any Evo's in stock or on display.
My take: The OneX somehow feels thicker and wider, as the Evo is styled to look like the thinnest slab of aluminum I've ever seen. I know spec wise they're very similar, but the Evo gives the illusion of being ridiculously slim. Like a knife almost. That said, holding a knife is kind of jarring. The oneX's rounded corners felt just a bit more natural and while the Evo feels more premium, it also feels more delicate/fragile. I'll say the OneX looks more modern and friendly with it's white polycarbonate and curved glass though.
The OneX had an HTC notes widget on it that I absolutely loved when I was using it in the store. It synced with evernote and everything. This...is not on the evo and I'm kind of really upset about that.
MicroSD slot is nice!
Mine gets significantly better 3G speeds than my old Epic4G. That probably doesn't help you since you probably get better speeds on AT&T, but it's actually usable on sprint where as my old Epic was just a brick when wifi wasn't around. So I'm pretty happy about that. Radios seem pretty good
I heard someone post somewhere that they were already getting some LTE in the outskirts of Atlanta, and it's RIDICULOUSLY fast! I'm jealous because I'm an hour away over in Athens and no such luck