I carry two phones. One on T-mobile and one on Verizon. Here in NYC and surrounding areas, T-mobile is the best overall. Each has it's dead spots, and usually one works when the other doesn't, which is why I don't use the same carrier for both phones. But I noticed, Verizon has more trouble spots nowadays.
T-mobile LTE whether 4G or 5G is always much faster with data.
Verizon has faster mmwave 5G than T-mobile. But mmwave is so fast, the difference in speed between the two carriers has no real world effect.
When dealing with some elevators or building basements, both carriers go out. It's rare that one carrier would work while the other doesn't.
T-mobile use to completely suck outside of city limits, but 5G has changed that, now I get good service in rural areas, which was only something to be had with Verizon. Also get good service in the West Coast, which before 5G service was spotty.
IMO, both carriers are solid, but you'll definitely get a better bang for the buck with T-mobile.