Two years ago I bought a T-Mobile hot spot for traveling and I can only remember a couple times we were without service on T-Mobile. I pay $35 a month for a 6GB plan and unused data rolls over to a cap of 20GB, plus my monthly 6gb. I keep it on all the time when we travel because my wife is on Facebook much of the time. T-Mobile also has a benefit called binge on where they do not charge you data when using Netflix. There has been a few times that T-Mobile would not handle the bandwidth to run Netflix. All things considered, it is well worth the $35 per month.
This post is opinion based on experience.
2015 Hurricane 27K
2013 Sea Ray 220SD