AT&T ticked me off. They claimed my new phone wouldn't work after they switched off ? 3g. I knew it would. Argued with them for months about it.
They sent me a new SIM card and a junk phone with VoLTE. They weren't supposed to disable my old SIM card, but they did on the shutoff date. No biggie; I ran through activation with the junk phone so I could switch SIM cards.
Except mobile internet didn't work on the new phone. They had entered the wrong friggin APN settings, and I couldn't fix this without rooting the phones. I swapped the SIM cards anyway, and went without 4g internet while I researched new carriers.
Ended up buying a Moto G Stylus, which is more powerful than my Samsung A10s and allows me to run most of my business from it. Specifically, it has more RAM, which I needed.
Because AT&T ticked me off several times over the years, I specifically went with Sprint/T-Mobile, through Patriot Mobile. While I'm sure the marketing hype for Patriot is largely a gimmick, I had a code that kept me from paying setup and switchover fees.
So far I'm happy. I'm not getting unsolicited marketing texts from AT&T anymore, and only the occasional political text. I can opt out of these any time, too, if I get tired of them.
Performance in this area isn't any better or worse than AT&T. They're shutting the Sprint towers down very soon, so we'll see after that, but I anticipate no problems.