I have Cingular, and with the exception of a dead zone at the end of my street, they are very good. Customer service has been excellent, too.
They NEVER send me the bill late, either.
My whole family has Cingular. We used to get excellent service, before Katrina. (We live just outside of N.O.) Now the service is terrible. We can call each other and get a recording saying the person doesn't have service, busy singal when no one is using the phone or even recordings saying you don't have to dial one to reach that number even though we had not dialed one. The service was really bad right after Katrina and only moderately better now. I'm not sure if other carriers are experiencing the same problems or not. I just hope it improves soon.