I've been on Verizon for about nine years, and my family has been with them for at least ten if not longer. It started with my dad having his work phone with them (he's a corporate CPA who travels a lot to meet with clients). Having Verizon has been really helpful for us with how spread out my family has been. We all started in Pittsburgh, PA. Then my brother went to college in Boston. Then my parents and I moved out to Minneapolis. Then I came to college outside of Kansas City (Verizon is one of the few to have LTE and 3G when you're driving through Iowa). My parents then moved back east to Baltimore. With all of that and my dad regularly traveling all over the country, Verizon's widespread coverage has been important to us despite the price. AT&T would probably be about the same, and T-Mobile doesn't quite have the coverage yet.
But honestly if I had to pay for my own phone, I'd probably go with T-Mobile. They're more affordable than Verizon or AT&T, and they offer a lot of incentives for young people like truly unlimited data, free music streaming, and rollover data. My boyfriend switched about a year and a half ago from AT&T and hasn't looked back other than when we drove through Iowa to go to Chicago. T-mobile has spotty coverage along I-35 and I-80. For the few times we leave the KC metro, I feel better knowing I have coverage on Verizon in case of an emergency.
I may try to convince my parents to allow me to pay for my line (and maybe bf's if and when we tie the knot) so I can stay on Verizon in the future. Right now it wouldn't be bad at $40 for my line access and $20 for 1/4 of the data bucket before taxes and fees. And now if I don't upgrade I qualify for the $25 BYOD discount if my dad responds to the email they sent.