I'm getting an iPhone 5 after three years with Android.
One of my biggest issues with Android is fragmentation. Even the SIII, hands down the best Android phone on the market, is running an outdated version of Android. I have a phone that's running a version of Android from 2 years ago...It's frustrating and a big issue with Android IMO.
The screen size of the galaxy is attractive, but feature for feature the two phones are similar. Galaxy has NFC, and more RAM, iPhone has a better processor and a much higher quality design/build.