I just went Nextel, and so far I love it, Verizion, I havnt dealt with much, but those commercials annoy the [censored] out of me....
Nextel so far has great customer service, dealt with them 3 times... (1. Registering the phone since i bought it from nextel.com, 2. I locked out my SIM Card on accident, didnt read owners manual, and experimented, 3. Was curious about Roadside Assistance since my parents car died... and see if i registered for it, if they could get a free tow to get car fixed.)
Nextel's service quality, ease to deal with, definatly is much better than AT&T/Cingular.

Just my $.02

Heard good things about Sprint too, which I heard is purchasing Nextel. Hopefully Nextel doesnt go down the drain like AT&T did...