Both have great hardware. The GS3 obviously has a bigger screen and a bigger battery and NFC.
Both phones are going to be fast, both phones are going to take great pictures for a phone. I really think that most of the hardware comparisons are a wash.
I have owned an iPhone 3G, a 3Gs, a 4, and Samsung Captivate, and now a HTC One X. I also work in iOS/Android development.
Before ICS, I wouldn't have been able to seriously use an android phone. I think ICS+ is usable although I am still not crazy about it.
I ended up going with the iPhone 5. I think the size should be perfect and the hardware looks great. If you don't like iOS, then don't get an iPhone. I think the Maps thing is a little overblown, because there are a lot of free Maps solutions out there that use Google Maps, Bing Maps, etc.
I also think NFC is kind of gimmicky. The stuff in the commercial about sharing playlists is something I would never do, because that involves signing up for samsung music service or something when I use Spotify. I also don't find myself sending files or movies to people that I wouldn't want to send over email or dropbox, so that they have a copy of it somewhere not on their phone. I am not saying that these features aren't useful for other people, but I just don't find them that useful.
Anyway, if you are indifferent about the screen size and NFC, I think it comes down to whether you prefer iOS or Android.