Ive had all three (AT&T, Verizon & T-Mobile), using a Winegard ConnecT testing them by replacing SIM card in different locations. Will be traveling from East Coast to West this summer or at least to Utah and Idaho from Florida. T-Mobile has an unlimited of 100 GB whereas Verizon only gives you 15GB which goes fast. With all of them it depends on Cell Towers, their maps will show coverage but in reality doesn't mean much. We're in Northern Michigan right now and the T-Mobile will range from 38% to 60% data coverage while sitting still. Verizon was a little better in same spot but still the same up and down. AT&T uses Mom and Pop former telephone companies up here and in some places even though map shows coverage there is non. I even call the companies and ask them to send a boost single and in some cases it helps but most of the time it makes no difference.
As always closer to larger Cities better it works, so far T-Mobile seems to be working little better and you can set streaming on your T-Mobile App to change download speeds to save usage. We've watched at least 10 to 15 shows and movies over the past several weeks and have only used 14 GB, that includes Internet use for email and other downloads. Right now it's not working so we're using a WiFi connection from a camp site. Don't know if there will ever be anything to a connection like Fiber to a router but it's better than a few years ago.