With any carrier choice it is very dependent on where you live work and travel. What is bad for me could be great for you because a particular carrier could have towers right near all the places you go.
If we are talking strictly 5G, T-Mobile is far ahead and has a better overall strategy than Verizon and AT&T.
They have a big jump with coverage and availability right now with their low and mid band deployment and can add more speed over time with high band mmWave.
Verizon's mmWave is virtually useless for general use and will never be deployed in sparsely populated suburbs and rural areas. It is being deployed in select high traffic, high use areas like business/tourist areas, large commercial office buildings, airports, stadiums and arenas. It is super high speed but has very little range or ability to penetrate objects. Verizon's website indicates it is available outside in select areas. There is no area in the entire country that has more than a few blocks of continuous Verizon 5G mmWave coverage. You can't use it in a moving car for more than a minute or so.
No carrier will be able to have nationwide coverage with just high band mmWave 5G.
Verizon will have to overpay to win the next spectrum auction this fall because everyone knows they are desperate for mid-band spectrum to roll out a nationwide 5G network.
T-Mobile already has a complete spectrum of high band mmWave, as well as mid and low band to cover the nation.
T-Mobile in 5G will be what Verizon has been in 4G. They will have the best coverage and reliability when looking to find and maintain a 5G signal.
I am still a Verizon customer because their 4G coverage is so much better (especially where I live) and practical 5G benefits are negligible at best.
This is why I am staying with my Note 10+ and sitting out the Note 20 Ultra.
But the next phone I get will have to be 5G and I will likely switch to T-Mobile unless Big Red gets a better plan for catching up to T-Mo