Working for a Cell Phone company, Verizon has the best Service. But they are expensive. Sprint runs on the CDMA network also so Sprint is capable of roaming on Verizon's Network. CDMA is also more reliable.

AT&T and T-Mobile run on GSM networks and they have outages everyonce in a while. Like Last week they had a 3G outage for a few hours. GSM also has some issues with being able to hop from tower to tower (so even though AT&T says they have less dropped calls, they don't).