From my experiences playing around with it, the S3 is a fantastic phone. If I liked Android better, I would strongly consider it. The Nexus 4 looks good too, but with Nexus 4 having only 16GB, no microSD slot, and merely passable camera, the S3 looks better despite lack of guarantee with regards to timely Android OS updates (and an uncertain future about when those stop coming).
That said, I still like iOS better, and I say that as a Nexus 7 owner. iOS simply has a more polished/more usable UI, higher-quality/wider variety of apps, and I've got a great music playback setup with AirPlay, syncing to iTunes, etc. I have an Apple TV and many Airport Expresses around the house. AirPlay mirroring is also useful.
To make me even consider switch, Android would need an Airplay equivalent (which can be used with arbitrary apps on the device) with matching TV and audio hardware to stream to. And this would need to be reliable, because it is amazingly reliable with the iPhone (not so much in OS X Mountain Lion on a Mac, though).
Going back on topic, I think the S3 is the current phone of choice for anyone who doesn't want an iPhone. I'm always excited to see when one of my friends or coworkers have bought one. I'm glad Android is competitive and want to see it succeed (rather than, say, Microsoft).