Galaxy S3 is nice, but I prefer the HTC One X and recommend that (you can get it on AT&T's network for a pretty decent price, not sure about T-Mobile). HTC, in general, implements their own interface on top of Android (Sense UI) and I find that it's a much smoother interface than the usual Android one. My friends who have the S3 have commented on that as well, but if it's not such a huge deal, then you're pretty much comparing oranges to oranges with the two.
Probably the best thing you can do is go to a provider's store and test them out yourself. Most Android devices out right now are all capable of similar things, it usually comes down to individual preference.
An aside: I really fell in love with Galaxy Note, even though it feels really ridiculous when you use it as, well, a phone. But dat screen. *-*