In NW Indiana, neither service is great. In fact, T-Mobile is worse than AT&T coverage wise. T-Mobile has way too many dead spots, according to people I know who either have or used to have T-Mobile. At least AT&T spent some money building their network, even if customer service isn't all that great. T-Mobile seems to be following Sprint's path from years ago signing more people than their network can handle that some areas have overloaded circuits. Now if you had Cingular before, signing up with AT&T now will most likely mean you'll end up with Cingular again. I say shop around, and ask people you know who they have and get feedback from them what they recommend. If you were in NW Indiana, I'd actually recommend Verizon Wireless over AT&T & T-Mobile, just because the network is well built up, and even more reliable in Chicago, unlike AT&T and T-Mobile, but not as bad with AT&T in Chicago as it is with T-Mobile.