What makes you say the One S is better? It has a 4 star review on Tmobile website where the GS II has a 5 star review. I am open to either. What do you like about it better?
Faster Processor, higher pixel density, superior design. I suppose Sense (HTC's skin on top of android) would be considered worse than Touchwiz (Samsung's skin), but the Galaxy S II is a whole year older than the One S, and the hardware shows it.
And like everyone else said, I'm pretty sure the GSIII was announced for all of the US carriers at $199 for 16 Gigs of flash storage.
If want to read a good review of the One S (or any smartphone, really) head on over to
http://www.theverge.com/. In my opinion, they have the best Tech News/Reviews.