I've been with AT&T for over a year now. I used to be with MetroPCS for years, but when I moved out to this area (southwest Michigan, near South Bend, Indiana), you could hardly find any stores that had MetroPCS phones and support. The service was great though, I do miss them. I switched to Boost Mobile and was a bit iffy, since they're part of Sprint and I remember hearing horror stories of Sprint coverage back in the day. Actually turned into okay coverage to my surprise.
I only switched to AT&T because my boyfriend needed a phone. Him and his friend were in a contract together with T-Mobile and the coverage in this area is horrible, too many dropped calls. They both complained to T-Mobile and said that they wanted out of the contract, because you can't even make a phone call most of the time and it never used to be like that before, almost like they took down towers in the area. T-Mobile wouldn't let them leave, but they left anyway.
Move to AT&T - My boyfriend and I did it in November 2013 on a whim. We were browsing Best Buy and I seen Galaxy S3's were 99 cents with a two year contract. With me having decent credit, we did it in my name. The coverage in this area is amazing, 4G LTE in such a small town. I've never had a problem with customer service, they even doubled our data from 10GB to 20GB at no extra cost (when you could call in, lie that you were leaving, and they would make you the offer). Now with rollover data, we're looking at a little over 30GB a month.
We pay over $170 a month for two lines, that's with my employee discount. It's only so high now, because we got two S5 Actives through NEXT. Before that, it was $120 a month.
They're not horrible, but as others have said, you need to shop around for a carrier that has good coverage in your area and the areas you go to.