I traded in my iPhone 3G for an EVO, and after a week and a half I'm still really liking it. I agree that Android 2.2 may not be as "polished" as iOS 4, but I like the customization and the new feel of it because I was a bit bored with the iPhone after two years. The fact that you can have widgets on your screen showing you actual data (calendar, weather, etc.), instead of just a grid of apps, is my favorite thing about the Android UI, and maybe the only thing I really think is better than the iOS UI.
The Android Market doesn't have nearly as much as the App Store, but that being said, I've only come across a couple of apps that I used regularly on the iPhone that I can't get for the EVO. I find browsing the internet to be a much better experience on the EVO, mainly because of the bigger screen, that I don't even find myself looking for mobile-optimized websites anymore.
As for the phone part, at first I missed the Favorites section of the iPhone, especially after the Favorites widget didn't work correctly on my EVO. But then I realized that I could put icons on my home screen (that look like contact pictures) that are one-touch shortcuts to the people I call the most. I rarely even go into the actual phone part of the phone now because my usual contacts are all one touch away.
So, for me, I think I would be happy with either the iOS or Android platforms, but right now I'm happier with the EVO than I would have been with the iPhone 4 just because it's different.