ICS is very good (almost feels like the beta test is over for Android). If you aren't heavily invested in iDevices it would be an easy switch. MP3ing and gaming is fine on Android. If you wanted to do anything like Office, Android is kinda lame right now, but Google has just bought QuickOffice.
The S3 has some nice features, like recognising when you are looking at the screen, but I'd go for the HTC myself. :
: Or wait for the iPhone 5, but that's just because of all the apps I already have and I really like how AppleTV works with everything.