As far as the "No coverage where I live / work" thing goes.
Just a well thought out one-week trial on T-Mo after >10 years on ATT.
* With AT&T, the towers by me are very overloaded, and leads to slow data and dropped calls. Because of the overload, they use all available spectrum, so the microcell's spectrum overlaps with the macrocell -- so during peak hours, even the microcell will drop calls!
* AT&T has no Wi-Fi Voice, so I'm just screwed at home
* AT&T does work at my office, though.
* AT&T drops calls while I drive in Miami.
* Data speeds, in general, are pretty low -- there are a few areas with good speeds, but generally it is slow and high latency, and things like Facetime Audio or Skype are impossible.
T-Mobile:
* Good signal at home (but like I said, who cares since I use WiFi) -- at least it's nice for backup.
* Dead zone inside office building
* WiFi Voice fixes the dead zone problem
* Great speeds driving around
* Facetime Audio works fine while driving (Over LTE)
* Phone calls on 5S (which are using 3G/UMTS) -- I have had a drop, but it is well publicized that T-Mobile is only really working on their LTE network at this point
* iPhone 6 has VoLTE, so UMTS issues are no longer a concern in Miami.
* HD Audio (even on UMTS) sounds much much better than AT&T's codec
* Places I have traveled in the last year include: NYC, San Jose, Atlanta, Phoenix, Las Vegas. T-Mobile has great coverage in all of those places. The one part of my travels that would have been a problem was a drive from Phoenix to Grand Canyon -- and even AT&T barely had coverage there, so no difference.
Yeah, going out to rural georgia or northern florida will probably be a problem on T-Mobile -- so for that reason I am keeping Verizon on my tablet for when I travel, and my wife is keeping AT&T (redundancy). For my phone, I will prefer T-Mo on my daily basis at home.
If I change my mind -- no contract, and I can always port away.