We've been happy Twigby customers for a few years now. You configure your account so that you get the talk, text, and data you need. They mainly use Sprint but Verizon is a backup when Sprint isn't available.
Husband's monthly bill is $13.93, which includes tax. He has 300 minutes talk, unlimited text, and 200MB data. My monthly bill is $18.76, which includes tax, and I have unlimited talk, unlimited text, and 200MB data.
You can choose to have it automatically upgrade you to the next level should you go over your allotted time. We've had great luck with them.