Since I cover the smartphone world and like to test handsets I had accounts with T-Mobile, Verizon, and AT&T. However, to save some money I just dropped AT&T and after reading the results of PCMag's Fastest Mobile Networks 2013 I may have to add them back to my arsenal.
PCMag conducted extensive real-world testing around the country using three Ford hybrid-electric vehicles with eight identical Samsung phones to test out the four major carriers. They were focused on wireless data and did not test call quality, dropped calls, or coverage areas. I don't make many calls myself and find wireless data to be more essential for my smartphone usage.
It's pretty clear that AT&T wins when it comes to LTE speeds while Verizon tended to win in the reliability testing. T-Mobile's LTE network is new and fast where you can find it, but they do have one of the fastest backups with their 42Mbps HSPA+ network. Sprint didn't win in any cities, but their LTE coverage is expanding.
30 cities were covered by the testing team and you can read the specific results for each city and by regions around the country. AT&T and Verizon are the most expensive carriers, but as you can see in the test results you get what you pay for in most cases.