I've had all the big carriers except T-Mobile at one point in time or another, they each have their quirks, I'm currently with VZW. Sprint struggles to give away service, their networks really do suffer and I dumped them for that reason along with their phone bands not being good for cross platform usage, I need to travel internationally with my phone and Sprint does not do well in that regard because they operate on different bands. I was pleased with AT&T for their pay as you go service since I was hardly in the US while I had them as well as I was able to use my phone I picked up in Dubai with their SIM, but once I returned I had a lot of issues with their coverage in areas I was typically at. The main place I couldn't get a signal was my gun range in the boonies where I absolutely feel having a signal is necessary, so I asked a couple fellow shooters who they had and Verizon was the only one with coverage, hence my switch. I very rarely don't have a signal anywhere in the mid-Atlantic region. The kids have T-Mobile, they bitch a lot about not having signal where I have one, gasping for their Facebook like a landed fish on a hot pier. Kids...
In my house where I live in the sticks and have a brick home, I had to start using WIFI Calling to get good service (highly recommend that for anyone who struggles to get indoor coverage where they have reliable WIFI), otherwise I often lose signal and smoke my battery if my phone is in my pocket as it is searching for signal, zero issues since I made that adjustment. I pay a bit for for my service, $90/mo for two lines and 6 GB data, I won't go to their unlimited since last I checked I couldn't WIFI hotspot with it and I need that capability, and my lady and I have yet to crack 2 GB in a month anyhow but we like the safety net if we need to.
I never have had billing issues with any of them, not a one, I always pay on time and make sure I understand my terms of service down to every line though. These days I buy my phones outright and stab in the SIM card, including internationally when I'm there for extended work. I refuse to have a contract with any of the companies, and I use a phone for much longer than they feel I should with their "upgrade" services they use to lure you to them.
Really though, the difference in cellular companies is like the difference in airline carriers - they all suck in their own way. It all comes down to what kind of shitty service a person is willing to deal with. Verizon and United sucks the least for me, everyone else has their own opinions and experiences.