Hard to offer any info unless we know where you live. Big difference between cell phone coverage east of Colorado/Kansas border vs. west of Colorado/Kansas border. Mountains and lack of people (aka customers) make for limited coverage by all providers. Tourists areas do attract more providers; one example is Yellowstone NP, a few years ago; nothing. Then all of a sudden a few years ago, I started receiving cell calls from people while traveling through it in certain locations within the park.
As someone who lives in ID (far from a large city...as classified as over 55K) and has traveled extensively in MT, WY, UT, CO and of course ID, the best out here for 4G LTE is undoubtedly; Verizon (or in my case, Tracfone a MVNO that runs of Verizon towers). Second would most likely be T-mobile. However, this advise is basically for those off the beaten path (major highways/interstates). All three providers generally have decent coverage off interstates and major highways. Get off those roads and it is hit and miss, and if a hit; usually it is Verizon; but not always.
This site allows you to overlay coverage maps over other coverage map. It is not as up to date as actual coverage maps directly from the provider.
https://fcc.maps.arcgis.com/apps/webappviewer/index.html?id=6c1b2e73d9d749cdb7bc88a0d1bdd25b
I just checked Verizon's coverage map on Verizon's site and can say it appears they have updated their map, at least for my area. A few months ago, where I lived, there was basically nothing; then last year they did extensive work on existing towers, added a few towers in my area and I have decent coverage in my house, that still drops out to the west due to some large obstacles called the Teton Mountains and lack of civilization in ID. It even show 5G creeping my way...slowly.)
Coverage maps are notoriously famous for inaccuracy. I remember a few years ago, camping with a friend and she had aa ATT phone and no coverage, I had my Tracfone phone and great coverage; including data. I was even able to check some coverage maps, and Verizon showed NO coverage where we were, ATT showed coverage. Go figure.