As far as quality goes, I have never had a bad iPhone. Gone through 3g, 3gs, 4, and 4s along with galaxy s II and several other android phones. Although the android phones are very well built and run things great, I have always had lock ups and problems with applications running on the android software. Just like Mac vs Windows, Apple never gives the headaches like other platforms do.
Android is unfinished business, with Wild West app store and uber-fragmented hardware (I own Android phone). iOS devices are more polished, and if you apply jailbreak (which is legal), your possibilities are limitless. The only thing that always had and will suck are the iTunes: terrible piece of software.
I am planning to get myself the new iPhone: great screen, tethering that works, better UI polish and included navigation. That's enough for my needs.
Get iPhone 5, trust me, you won't regret it. Everyone can make bigger phones better, but not everyone can make smaller phones better - Apple.
It's the world's thinnest smartphone and is completely solid, made from aluminum and glass. S3 doesn't even come close to it - I mean plastics on the body? Ergonomics wise, iPhone simply is the best.