Isn't the iPhone 5 due out in a month or two? You may want to see how that turns out.
I still like my Galaxy Note.
I think October was the most recent I heard.
Personally, I'm not at all interested in an iphone, mostly because apple products don't play well with others. I'd have to convert all my music, for instance. Plus, I basically live my life through google, so android is pretty seamless.
There's a new version of the Note coming out at the end of this month. That's the one that's comparable to the s3. Personally, switching to the s3 from my original model galaxy is daunting enough. If I think the s3 is huge, no way could I handle a note.
But, as I said before, it's generally cheaper to buy a full price (ie unlocked, can be used on T-Mo) phone when combined with the far cheaper monthly prepay plan. Of course this assumes you have the $630 (current list price for the s3, probably similar for the iphone after a couple months) available. It also assumes a single person rather than a big family plan.
However, if that's your case, you'd save about $400 over the course of a 2 year contract (depends on your state's cell phone tax) if you pay the upfront cost of the phone and get the cheaper monthly plan.