Studies like this are nice, but in the end when it comes to coverage (as opposed to perks) it comes down to where you live, period.
Anyone can find an area where a particular carrier has good or even great coverage and the others have little to none. The important info is which is the good one where you live and/or spend your time.
In my rural town, TMobile happens to have a shiny new UB-5G tower near my house and I can get speeds in the hundreds of Mbit/s range. The other two don’t even have 5G here. TMo is nearly as fast as my 400Mbit Suddenlink cable, and it’s so much more reliable that I’ll often turn wifi off if a video conference is flakey.
The next town over also has a new TMo tower and I have a decent signal while people who live there and have Verizon or AT&T can’t even get a signal half the time.
On the other hand, 5 miles up into the hills TMo has no coverage at all and Verizon works fine, so if I lived there (or needed to spend a lot of time there) I’d make a completely different choice.
That said, I actually switched to T-Mobile because they offer free data roaming in Japan where I spend a few weeks a year and my significant other spends a couple months. That feature has nothing to do with their network and simply isn’t available from the other carriers, and is an expensive hassle to do any other way.