I've got to admit that I'm biased as I moved away from iPhone a few years ago - I had a 3GS and I was annoyed at how quickly aspects of it became obsolete.
I prefer having removable storage that I can more easily back-up, and not being tied to my desktop machine and iTunes as the portal for all updates.
Also, since I work in audio, it's terrific to be able to more cleanly sync with Google docs, download and open zipped files, etc.
I also like how the GS3 sharing options (especially for photos) are super, super flexible. And once you go to a bigger screen, you really feel the difference.
I miss the Apple apps base - which is still second to none, but I still enjoy it via the iPad, and I'm pretty happy with the decision.