I'm cheap and hate contracts so I was on Virgin for about a year. Downside was they are on Sprint's network and I wouldn't have coverage up in northern AZ. I recently switched to Republic Wireless and have been very, very pleased. They utilize wifi calling as well as roaming so I now have coverage everywhere I need it. And at only $25/month for 3G ($40 for 4G). Downside is you have to buy one of their phones, but I really dig the Moto X.

The Moto X does multi-tasking, so you know, booyah.