Three years ago when my Sprint contract ended I compared the other networks. T-Mobile had the smallest footprint. At&T and Verizon had nearly the same. much larger footprint. One of the major magazines (CNET, IIRC) compard those two. At&T had higher average speeds than Verizon, but also had more dropped calls, dropped data connections, and dead zones than Verizon. I went with Verizon largely because none of the places I went to regularly seems to be Verizon dead zones. I've been very happy with them, but I realize that it's more luck than anything else that my life just happens not to take me into any Verizon dead zones.
When choosing a cell service provider it's important to check those 4 companies: AT&T, Verizon, T-Mobile, and Sprint. Why? These companies own the only physical nationwide cell networks. EVERYBODY uses one of the 4, no matter what your phone or your bill says. ALL the other companies use one or two of these 4 networks. SimpleMobile uses T-Mobile. Virgin uses Sprint. Google "MVNO" and you'll see.
Jim