You might want to check out Consumer Reports. They released their cell phone issue a few months ago. They break it down city-by-city so you can get more detailed information on the coverage quality. Here's a brief article about it:
http://www.consumerreports.org/cro/e...service-ov.htm
"Alltel and Verizon got high marks across the board for connectivity.T-Mobile had relatively high satisfaction scores, but customers experienced problems with lack of service in some cities. Subscribers also highlighted problems with AT&T for gaps in service and static, and with Sprint for dropped calls. "
"Alltel, T-Mobile, and Verizon were the better choices in a bad lot for customer service. "
AT&T and Verizon plans have identical price structures. I've had both and greatly prefer Verizon, especially in DC area (service in the metro!).