They all kind of suck in a way. T-Mobile used to have the best plan with their 1,000 minute plan. Verizon is the most expensive even though they have the best connection. The good thing about AT&T is that they have free calls to other AT&T subscribers and in their case it's really worth it since most people have AT&T. So I would probably advise you to go with them.
If you are not making most calls to other AT&T subscribers and I wold say go with T-Mobile. You get a little more minutes for the price and their rates like texting are a little lower as well. AT&T and T-Mobile both don't exactly have the best connection.

