I use Straight Talk, have used it for years, very satisfied with service, my version runs off Verizon.
Don;t go to Wal Mart, go to their web site, and buy a phone. I buy a one year old (in terms of introduction date) refurb that comes with a full factory warranty. You can spend as little or as much money as you want - they still sell flip phones for like $15
J just bought a Samsung A50, a 2020 introduction for about 25% of new, does everything I need it to do.
I have service with Cricket. It runs on the ATT network. No complaints at all and it is cheap.
New service out there called Mint that is advertised as $15 per month unlimited. I pay $25 but I have five phones with them @ $25. Fewer phones and the price/line goes up a little.