I use ultramobile.com, a T-Mobile MVNO. $19/mo, bring your own unlocked phone.
The only problem with TMO MVNOs is that I haven't found any that will hop on to ATT's towers when there's no TMO tower in range. TMO's own prepaid would, the last time I checked, at least for voice and SMS (but not MMS or data), but their MVNO's will not.
When I first moved out of The City, the first place I lived was within eyesight of a TMO tower, so I used TMO. It worked out fine because although TMO's towers were rather sparse, the phone would hop on to ATT when needed, so at least I had voice and text pretty much anywhere I went. But when I moved to my current home, there was only VZW service, so I switched to ST over VZW. That was fine save for the then-limited selection of phones and the prohibitions against tethering or hotspots.
When ATT planted a tower nearby, I decided to jump ship. It wasn't easy because the sales side of ATT's system didn't know that the tower existed, and ATT's policy was to decline potential customers if the company didn't believe they had service at the customer's location. It was pretty bizarre. You could buy a GoPhone off the rack at Dollar General and then call ATT customer service from that phone using ATT's signal, and they still couldn't activate you if the ZIP code you provided was not in their database of places where they had service. Their system wouldn't allow it, and the CSRs couldn't override it.
The policy was there for a good reason: to prevent customers from activating service that the company didn't think it could provide. But the implementation was bad. The sales side's databases didn't update right away when new towers were planted, and the CSRs had no ability to override.
The simple workaround was to hang up and then activate the phone using the ZIP code of Some Other Place where you knew that ATT knew that they had service. Then once the service was activated, immediately change the address to your real one (or to just leave it be if you planned to use store-bought refill cards to pay the bill rather than paying online).
But to do that, I had to actually get a SIM card, which their system wouldn't allow to be mailed to an address where they didn't believe that they had service. That left me with two choices: Either buy a cheap GoPhone at the local Dollar General just to get the SIM card, or make the 50-mile drive to the nearest AT&T store to get a SIM card. I made the trip and activated the phone.
So yeah, it was a bit of an adventure. But since then, the service has been both cheap and flawless, so I have no complaints.
Rich