I recently upgraded to the Sensation XE after my Desire went FUBAR. At the moment it feels pretty slick, it doesn't have the android crashes as much as my desire, and yeah, it works pretty well. It's also nowhere near as big as the Nexus or other phones, which is a plus in my mind. Battery life seems pretty good, but not great. I still charge it nightly because otherwise the second day of use can be pushing it a bit.
Saying that, if my Desire is anything to go by, the updates won't be particularly well optimised by HTC. From my experience, Apple are much much better at making sure that updates are going to run smoothly on their tech that is already out, and if it's going to cause you to lose some experience you won't get it. HTC seem to just focus on the next thing along. To be honest, after a year of having a Desire and the software updates causing so many issues I wouldn't be surprised if I have the same issue with my XE in a years time.
If it was up to me, I'd probably get the iPhone 4. Hell if I'd been able to upgrade to an iPhone 4 over the XE then I would have done, whilst the XE is a slick phone at the moment, I'm not quite sure it'll be that way in 6 months time...
kd