I use Verizon JetPack with a prepaid plan. With the prepay plan I can just turn it on when I need it. That way I don't have to pay every month for a service I'm not using. I usually just purchase a 3GB 30 day plan whenever we decide to travel.
I also like having my wifi service from a different carrier than my phone service. Many times I've found I have service on one but not on the other. By having 2 carriers I'm usually able to have service from one or the other. More often than not, I have both phone and internet but in some remote areas I only get one. My phone is ATT and JetPack is Verizon.