Did you post this in all the carrier sub-forums?
I did. It was the only way I could think of to get a well-rounded response.
I, myself am a bit torn:
Sprint
I still have unlimited data with Sprint, but I'm moving to the Dallas area and Sprint is a little spotty in coverage there. Sprint 3G speeds are consistent, but I'd like a 4G option that works. For a family plan with 5 smart phones, I haven't found a better deal than Sprint's.
AT&T
AT&T is at the top of my list right now because of their dual "4G" technologies. When you're not in LTE coverage (Dallas is AT&T HQ, so that may not be an issue), there's a good chance you'll be covered by a nice HSPA+ network. AT&T family plan can be cheap if you match your plan to your needs. If I put my mom on a dumb phone, it could actually be cheaper than Sprint, but with a lesser plan. I've heard people have problems with AT&T with dropped calls and the like. Probably my first choice considering the Dallas area (Plano specifically). Being able to switch phones by switching the SIM card in/out is nice, especially because you can use a smartphone without a data plan.
Verizon
Definitely the best coverage overall for voice, 3G and 4G. I don't like EVDO 3G speeds or the price of Verizon's plans. I also don't like the battery drain of LTE. When Verizon is VoLTE, I think LTE phones will be a lot better on battery life. Or perhaps they'll figure out how to make the LTE radios more battery friendly.
T-Mobile
I used to have T-Mobile and I was always happy with them. Their HSPA+ network is nice, but with no news of LTE, I'm not sure I'm ready to sign up for 2 years. Their prices are great in general. One hangup is that my wife would prefer to have an iPhone on our next carrier; although she is willing to go back to Android given the right size, quality, and speed. Also, having a SIM card is convenient, especially if you want a smart phone without a data plan.
I definitely see the pros and cons of all four carriers, which is why I wanted to hear everyone else's opinions.