Did a big trip from Texas to Key West to Connecticut to Texas last year.
We stayed at a lot of COE, USFS and military base campgrounds. And out of the way spots in the Northeast.
Verizon ran about 35% good coverage.
ATT ran about 45% good coverage.
When you look at a coverage map of an area - it may show 'great coverage' but a campground might have no coverage. It always amazes me that a COE campground in the Dallas metro area has no usable Verizon signal, yet a half mile away at Walmart - great signal.
Yes, we had no cell or hot spot coverage about 20% of the time, which is a lot better than west Texas or the mountains of New Mexico.
Be aware of terrain. If you are surrounded by mountains and down in a valley - your chances of getting coverage are low.
If you are back in the woods 'far' from civilization - your chances of coverage are low.
If you want to stay near interstates and medium to large cities - your chances of coverage are high.
Yes, we have both, and take both with us as full-timers.