I have already tried Android (HTC Inspire 4G). I tried it for 3-4 months and came back to my iPhone 4.
Battery life on the Inspire sucked, less than 9 hours. Unacceptable. I tried everything. Turned off wifi, gps, bluetooth, 25% brightness (which sucks to use a phone at), custom ROMs meant to increase battery life, etc.
Overall, Android is great but has so many little problems from my use. Nothing major but the polish is not their like iOS. Obviously, I enjoy some aspects of Android a lot more than iOS but not nearly enough of them.