In general with MVNOs, you lose domestic data roaming, and international roaming is expensive/non existent. Whether that is important to you or not, only you can answer.
Ting is a MVNO that prouds itself on having US-based support with no waiting (not offshore), and a business model that doesn't try to screw over their customers (crazy, right). I can attest to both of that.
Ting uses T-mobile's OR Sprint's networks. But only one at a time, you need to chose for each number. Unlike other MVNOs they don't throttle you nor they limit you in any way in regards to tethering or whatever you want to do.
They are not a cheap MVNO, there are others far cheaper if you use a lot of data. But I still prefer them. However, they will still be cheaper than Verizon.
Go to their website, there's a calculator that tells you how much you'll pay. You can have any number of devices (phones, tablets) on the same account, the minutes, data, etc pool together and you'll only pay once. You pay exactly what you use, there are no "plans", etc, but it's postpaid, not prepaid (huge plus to me).