I think AT&T overall is one of the worst carriers period as far as pricing and corporate greed. There's nothing wrong with being profit-driven, but they take it to extremes sometimes IMHO, compared to the other carriers.
I have experience with Tmobile and think they are one of the best for in-store customer service and PRICING (I was paying about 30% less a month with Tmob using a comparable plan).
However, I am sticking with AT&T even though they are being horrible and not supporting mobile hotspot due to a lack of official 7.1 release (fixed via the tether.com app) due to their national coverage map. I now travel more often for business and personal trips throughout the USA, and there's a certain relief to be able to tether my phone to my Macbook in Wyoming or Montana versus being limited to big metro areas for voice and data.