Well i'm currently w/ Cingular, but have been w/ quite a few other companies... (Sprint, T-Mobile, Voicestream, Verizon/Powertel)
My honest opinion? They all suck.... 🙁 I've had various billing and receiption issues with pretty much all of them at one point in time.
Take for example T-Mobile: My first two bills were over $650, as they not only fergot to code in ANY minutes into my plan, but after i called following the first bill, they did it again the second month.
Cingular has problems removing and adding features to my plan. Added a service for a month, took it off the next, yet i had to call for the next 5 months because every month, i was charged again.
I am however staying with Cingular for the indefinate future...
They were the ONLY cell phone company that kept their towers operating around my parents house right after the hurricane (no power for over a week).