I start with the recent history of my cell phones only going back about 8 years or so.
We used Sprint because at that time they were the only carrier that would allow me to use my phone both at work and home without paying a roaming charge one way or the other. Constantly had dropped calls and service at home usually worked, but once in awhile you wouldn't have any service.
Probably 4 years or so ago we switched to AT&T Wireless which was then bought out by Cingular which is now back to AT&T.

Much better coverage no (or very few) dropped calls. Works great at the house - even in the basement. I've driven all the way from work to home (over an hour) and talked to Monica the whole way w/o dropping the call.
We did run into an issue with them a couple of months ago. We had an old checking account we were trying to close out that was stored in their account. When Monica paid the bill, she entered our new account. It still charged the old account, just so happened there was enough money in the account to cover it. The next month I paid the bill. Same thing happened - except this time there wasn't enough money to cover it. The bank charged us NSF. By the time we knew what was going on and got in touch with AT&T they had sent it through 3 more times. $100 in NSF fees. I got them to credit our bill for the NSF fees. Then all of sudden they said we had a late bill and turned our phones off. I guess our bill was something like $102 so we owed $2. So I paid it and go the phone turned back on. When we got the next bill they charged us a $25 Returned check fee and a $36 reactivation fee. I was really pissed. I did get them to take those charges off the bill. Funny their website worked the last couple of times we've used it.
As far as Verizon goes, I've heard good things about them from the people in Columbus and that is what the company has switched to because of their coverage area. But for us at the house, if we go outside, turn around in circles, hold our head a certain way, you can make a call badly digitized call. We had a delivery person at our house (Sears) where they have to call in and "report" the delivery. It was funny watching him try to make that call.
When they were building our house, the excavator that did the footers and basement walls had Nextel for all of this guys. They couldn't get service at all. I guess Sprint still doesn't have Nextel on the same network. But their office would call Monica's cell in order to reach their onsite foreman.
I would be nice to have Verizon as we could then just add our Suburban as another phone to our plan and not have to pay for minutes - which I won't be doing because of the price GM wants for minutes.