It's funny how nice these corporations seem to act when breaking into new markets. Ask an european about T-Mobile and he will tell you pretty much the same stories that you tell about AT&T.
It is my goal to support the most desirable company in any market. Don't think that I would hesitate for a second to change carriers if T-Mobile stopped being nice, competent, and helpful and AT&T stopped being jerks and offering reasonable plans and policies. Vote with your wallet and all that, and right now, T-Mobile is the only cell phone service provider that I am aware of that doesn't suck in my market.
The tragedy - at least in my experience - is that in the long run they're really all the same. "Trust us, we want only your best! (your money)".
I can only second kevingadd's advice to try and not tie yourself to one with a longterm contract. The fewer customers they have locked in, the more careful they have to be about not pissing them off.