I came to the HD7 from the EVO. They are very similar. I haven't spent enough time to really do a fair comparison, but here are some initial impressions:
1. Size. Both phones are very pocketable, but I prefer the HD7's slimmer profile.
2. Responsiveness. Comparing Android to WP7 is comparing apples to oranges, but on what is basically the same hardware, the HD7 feels much more responsive and fluid in swiping, zooming, pinching, etc...
3. Kickstand. The kickstand on the EVO feels MUCH more substantial than the one on the HD2. I'm not worried, but it is definitely thinner on the HD7.
4. Capacitive buttons. These work great on both phones.
5. Camera. I might be in the minority, but the EVO took the best still pictures of any camera phone I've ever used (Palm Pre, iPhone , iPhone 3G, iPhone 3GS). The video quality however, was utter crap. I haven't taken enough pictures with the HD7, but pictures taken outdoors seem quite comparable. Video quality is definitely smoother at 720p and a consistent 24fps. One question: Why does HTC continue to make phones that have the camera lens resting directly on whatever surface the phone is rested on??!? This is a design choice that makes no sense- it begs for the lens cover to get scratched up.
6. Screen. I do notice a grid of dots (similar to what I noticed on my Palm Pre), but these are not noticeable when the screen is on. The quality seems quite comparable between the two. As an added bonus, on both phones that I have had- perfect screens- no dead pixels!
7. Camera button. I love having the camera button and have not had any problems with it. I certainly wish my EVO had this! It is incredibly annoying however, that the camera software (both still and video) does not retain its settings after you exit the app. Hopefully this will get addressed in a future update.
8. Sync Software. While not a hardware issue, I really miss having a choice of sync software to use with my EVO. The Mac client is slow, slow, slow. Hopefully this will change as it comes out of beta.
9. My biggest gripe- speaker volume. The EVO had a loud and powerful speaker. The HD7's is weak and tinny- not nearly enough volume. Apple addressed this in one of their iPhone updates and I hope that Microsoft will address it in one of theirs...