After struggling with RV park wifi and cellular MiFi devices, I finally took the plunge and bought a high end cellular AND wifi router manufactured by Peplink. Mine is the Pepwave Max BR1 LTE. It utilizes up to 2 cellular sim cards from any of the big cell companies. They make several other models that are dedicated to only one cell provider that cost a bit less. We prefer Verizon because of their superior coverage. What makes this system so great is the addition of a "5 in 1" roof mounted antenna. The 5 parts of it are 2 cell antennas, one wifi input, one wifi output (WAN) and a GPS antenna. I can reach RV park Wifi signals from some pretty incredible distances that our laptops cannot even "see". The same goes for bringing in weak cellular signals. It works incredibly well. Some of the setup menus can be a bit daunting for someone who is not very tech savvy, so buying one of these systems from a well known company with excellent tech help is critical. The Pepwave cost about $500 and the antenna was nearly as much. Not cheap, but if you want something that is far superior to WiFi hotspots and MiFi type devices, you get what you pay for.
I did have some issues getting the Verizon sim card to work, but the Peplink tech guys went out of their way to log into my unit remotely and fix everything. Very good customer support, unlike where I actually purchased it. From my searching on the web, I think that the 3G Store is probably the best source. They have a huge database of information on their web site that is only available to their customers.
We are spending about $120 a month for 22 GB of data, which isn't cheap. But being full time, we like to stay connected without using lousy WiFi hot spots. It remains connected 24/7 so my wife very often is on her iPad going down the highway without a bit of signal loss.