Actually, Nextel has the worst customer service. AT&T used to be the best but have dropped a few notches. Verizon is now number one. I have no complaints about AT&T. They always replace my phone, no questions asked. The coverage is excellent when I travel and my company pays for the service which is the best part.
I have friends who have Cingular, SprintPCS, Nextel and that new Metro POS (piece of shit) and they all complain about coverage or dropped calls. If I had to recommend one, it'd be Verizon. BTW, next year, AT&T will also have "push to talk", same as Nextel. Verizon already has it.