First thing is to find out who has coverage where you are going. Verizon is the best, then AT&T. The other two it may be best to be in a city or near a major highway.
For us trying to get signal in the Rockies, there is no one carrier that can be depended on exclusively. You may have coverage on one carrier and move 5 feet and have it on another if it is there at all. So I got us coverage on all of them for as little as possible.
Our main Phones are Cricket on AT&T with 10 gigs each and a hotspot on the phone. $65 a month each.
On T-Mobile we have a hotspot with 5 gigs and unlimited streaming with Binge on. it's 700 band is the only advertised LTE up there. $20 a month.
On Sprint we have a few hotspots from FreedomPop that give up a gig of data each for free a month. We also have a phone each from RingPlus that have hotspots and 3 gigs each for $10 a month.
Last up is the Verizon hotspot with unlimited 3G data for $5 a month.
Because out sites are so remote we also have a Wilson Sleek signal booster. It won't create a signal where there is none but it will make a weak signal usable.