RE: T-Mobile
The first thing that I would say is that phones are generally better now; you also don't have to buy the phone itself from T-Mobile. The only potential benefit to buying a phone directly from them (if the phones are the same price) is that they will often offer to split it up, interest-free, and add it to your bill over a period of six or twelve months. I don't know if I'm necessarily inclined to avail myself of that, probably not.
That aside, I'd just go to the Apple Store, and then to T-Mobile, and see where I can get the cheapest phone. I'm pretty partial to iPhones as I have never had a problem with one. My Google Phone absolutely sucked; though it was pretty good for the first year, or so. What happened was they did some update that turned the phone's IP Address to all 0's, as a result, I couldn't make phone calls or do anything unless I was on some kind of WiFi. Obviously, my phone was outside of warranty, so they wouldn't do anything about it, despite that it was their update that did it! I would have been on AT&T at the time, but the problem had nothing to do with them in the first place.
My only complaint with AT&T is that they were too expensive and I didn't find the service/coverage any better with them than it was with T-Mobile.
You're probably aware of this, but T-Mobile and Sprint merged and is now all T-Mobile. T-Mobile is no longer a discount cell service company and are, in fact, the third-largest provider in the U.S. (market share) with #4 not even being in their remote vicinity. People also seem to like T-Mobile the best these days:
https://clark.com/cell-phones/best-c...one-providers/
I don't think you'd have a similar issue with them nowadays, but you could avoid any possibility of that simply by purchasing your phone elsewhere.