In South Louisiana I have had all four: Verizon from 1999-2010, Sprint From April 2010-April 2011, and AT&T From April 2011 to now. Now not counting Data, just because i didnt have it with verizon, my order is as follows:
Voice: Tied Verizon/Sprint. Both worked anywhere I went in South LA/Southern MS. From the woods of Amite to the woods of Wiggins, I was never without coverage.
AT&T, not really having it long enough to make a real accurate report, but the three months I have had it I have dropped more calls than all the time I was with Verizon AND Sprint COMBINED.
Data: Having never had Verizon Data, all I can speak of is Sprint and AT&T. And my experience is, there's a reason why Sprint's data is unlimited: You'll be gray waiting on it. Its impossible to USE more than a gig or so a month unless you stream 24/7. Best speed I ever got on my Evo was just over 1mbps. AT&T, OTOH, smokes. 3mbps/second is common, ANY time of the day.
T-mobile...well...I use them for prepaid for my Mom. Enough said about that. Nothing to write home about. It does work. Most of the time.
And your comment about CS, well, I haven't had any decent CS since the early 2000's when ONE person took care of me at the Verizon store. ANY time I needed to call ANY of the providers, including AT&T, they suck. I currently am developing a pretty good relationship with a person in the AT&T store, she has been most helpful, so far. Its been three months since I applied for my corporate FAN discount and I still don't have it, though. And she has promised me every time I will on the next bill. She did make sure I got a credit for the missed months so far, but she has been unable to get it applied to my account as of yet.
Good luck.