I had a whole big bust-up with Sprint this past summer about bad customer service and left them after five years. I'd never had cause to deal with their customer service before, but it was far worse than Time Warner, Allstate Insurance, or even Bell Canada, to name three companies I've had my share of issues with in the past. Sprint essentially lied about stupid shit that I was bound to find out they were lying about, and it was stuff that wouldn't have made me angry if they'd told the truth. When I called them on the lie, they tried to bully me, lied to me some more, tried to lock me into a new contract, etc, etc. So I'm now crusading against Sprint, and advise getting out while you can...
I'm now with AT&T. Haven't noticed any less network coverage than I had with Sprint. I can get a signal inside the R Bar with AT&T, which I never could with Sprint. No big problems with dropped calls, although I honestly didn't have huge issues with Sprint on that. Haven't dealt with customer service beyond signing up for service, so I can't say if they're any better than Sprint on that. But no problems so far.
Also, dunno if this makes any difference, but I travel to Canada a lot, and Sprint absolutely raped me on extra charges for using my phone up there (that is, when it worked at all, which was only part of the time). I went to Toronto and Waterloo after getting my AT&T phone, and not only were there no service gaps, my bill was only $5 higher than usual. That's a huge plus for AT&T from my POV, although it may not matter to you.