Verizon. They are hurting my wallet and I don't know if it is worth the hassle. My contract expires in January. I may look at T mobile(yes, again!!), Sprint, or AT T.
Check PagePlus (https://www.pagepluscellular.com/ )
they are a MVNO that uses Verizon towers. There are a few limitations like it is 3G service, 4G phones have to be flashed and phones that were originally on Verizon's own prepaid plans are not allowed. But you are likely to be able to use a phone you already have. You can put a smartphone on any of their plans and being prepaid without a contract, if you don't like them, you can leave anytime. I have found them reliable.