Open wifi is notoriously fangerous and horrible at the same time. They might be OK for general emails, but there is no way I would allow a hacker access to my personal information over an open system. Verizon has by far the best overall coverage. With their new data plans they made it easier to choose and use.
A mifi card will cost you extra whereas any decent smart phone will eo the same thing for less money. Unless your a huge power user, all you need is around 12Gb a month for general bill paying, light web surfing, and family emailing.