while i originally wanted an android phone (because i knew my provider would never have a windows 7 phone, which i like, any time soon), my provider offered a great deal for the iphone 4, which i couldn't pass up. One thing android may never be able to catch up to, is the number of quality apps, especially games. my iphone is jailbroken, so i also have nes, snes, sega, gb, gba, n64 and ps 1 emulations. the daw control apps are nice (cubase ic, ac-7, omni live, etc), but i don't have wi-fi to take advantage of it, while the daw apps for iphone are pretty cool. android is supposed to get more in the future.
what turned my off of android a bit, was the heightened possibility of permanently bricking your phone. This is more important when you realize you're dependent not only on the manufacturer, but also your provider, to release the latest android update or version, if they even bother. some those who have rightfully jumped the gun because of that inaction/laziness, have at times fucked their phones up.
the lack of flash did bother me when i was still deciding, but i have alternative apps and i haven't been affected by the lack of flash so far.
phone-wise, android, and windows, have better phones, bigger screens, etc, due to there being more manufacturers, some of them are drool-worthy. i'm very curious about xperia play, the playstation phone using android.
i don't think you can go wrong with either android or the ios4 (while i like the windows 7 os, they won't be able to catch up to either, which might hinder their commitment), you just have to be more informed on which android phone to get, which version they have and will update to, and which ones to avoid.