Actually, US Mobile offers Verizon, ATT, and T-Mobile. You choose. What’s cool about this is that you can even switch between the networks (depending on your plan, switching is either included or a $2 charge). I don’t know any other vendor that offers this feature.
I switched to US Mobile from Mint a few months ago. It’s been great so far. I don’t care which network I use since all three have good coverage in my area, so I am on ATT as that offered the best deal when I signed up. Unlimited data for ~$22 per month for a year (they’re offering a better deal today of just $195 for a year for their premium plan, which includes a watch sim, unlimited hotspot data, free network transfers (ATT to Verizon, etc) and more international data).
I promised myself years ago I wouldn’t commit myself to a provider by having them subsidize my phones. I also keep my phone for 4-5 years so it pays to just buy it outright (or at 0% interest over time, if offered at time of purchase) and choose my carrier. I absolutely want the ability to switch providers whenever I want without having to buy out a phone and deal with unlocking it, should service quality change, etc.
These carriers, like airlines and hotel/timeshare programs, have no loyalty to me. I see no reason why I should have loyalty to them.