You clearly aren't living in the US. Every carrier has their issues in certain locations. The US is large, with states larger than some countries! I live in Texas, about the size of France.
at&t isn't all that, either. VERIZON is the best carrier for service across the board, but ask anyone, and they tell you, the crown jewel is Tmobile in the US. Pricing is much more fair, they are honest and up front about everything, including areas where they aren't so strong in coverage, etc.
Since the failed merger with at&t, TMo has acquired lots of spectrum as part of the breakup, and their network today is the fastest in most areas, both in HSPA+ and LTE, and coverage is closer to par with the big 2 now. Its not the fastest growing carrier for no reason, my friend.
Cricket sucks. Throttled pieces of bug legged trash. MetroPCS is better, and on TMo network. I'm in the US. I cover this industry here. Trust me, the old marketing messages about TMo are no longer true.