AT&T Mobley mobile hotspot (no longer available plan), also some times a T Mobile hotspot from my wife's work. 23,000+ miles of travel over the last almost 4 years, ranging from Louisiana north to Missouri, west to the Grand Canyon, and north west to Yellowstone NP. Overall good coverage probably 90% of locations, with little service in Yellowstone or at the Grand Canyon with either network. Some other service gaps, but those are usually in mountain valley areas, one example of service on T-Mobile and no service on AT&T (phone or hotspot) is Gila National Forest in NM.
2002 Safari Trek 2830 on P32 Chassis with 8.1L