You know which carrier I really enjoy after having used all of them. (Even though it was still Cingular at that point)
T-Mobile
And now I'll list the reasons why.
Verizon - terrible customer service
Cingular - Thought my plan was nationwide & called to double check before I left for vacation. It wasn't. Got a 400 dollar phone bill that month. Couldn't get it lowered at all. That went to collections.
Sprint - I can't say much about them as I only had them for a year & never really talked to customer service reps.
AT&T - Couldn't even get a plan without paying a 600 dollar deposit. Ironically, thanks to the Cingular bill going to collections.
T-Mobile - Walked into the store. Walked out with two phones/lines for both my wife & I without paying a deposit. We chose the option to pay ahead for on our bill because we were short on cash at the time. So if my phone gets shut off due to non-payment, the bill gets lower every day I don't pay it.
For instance: Original bill is due on the 1st at 100 dollars. If I wait until the 7th to pay it, it drops by 25 dollars. Now I have to pay 75 dollars.
Pretty sweet deal, if you ask me. I'll deal with their spotty coverage for that. But, honestly, since moving, I haven't had a single problem.
I also really enjoy their customer service. I just hope they never get greedy like AT&T & Verizon.