Being that Sprint MVNO Chit Chat Mobile no longer offers unlimited data, the best Sprint MVNO I can recommend now is FreedomPop. For $20 a month you get unlimited talk and text as well as 1 GB LTE data that gets throttled to 3G but is unlimited once you go over the LTE threshold. In fact his might be the best all around MVNO period, at least in terms of value and price. Be aware of their T.O.S. though as they will charge you an extra $10 for 1 GB of data once you get within 100 MB of your plans limit if you are not unlimited. For more on FreedomPop see my previous post or the Sprint MVNO's page.
The best T-Mobile MVNO is not an MVNO but rather T-mobile prepaid in my opinion. At a cost of $30 a month for 100m talk and unlimited text with 5GB 4G LTE it's hard to find a better deal anywhere. With more apps such as Google hangouts (at moment for iOS only) and FreedomPop offering unlimited free phone calls over data and WiFi, we find 100m of talk manageable. The main drawback of this service is that T -mobile doesn't offer the robust coverage that AT&T and Verizon based MVNO's do. Furthermore voice calls over data (VoIP) will drain your battery a little quicker than traditional calling.
The best Sprint MVNO with unlimited LTE and a roaming agreement with Verizon is ChitChat mobile. At a price of $45 a month, you get unlimited LTE data, 250 minutes of talk and unlimited texting. While 250 minutes of talk may be considered small by some, as mentioned above, the low amount of voice minutes can easily be circumvented if need be by various apps.
Now onto the best Verizon MVNO. This is a close one between Net 10 and Straight Talk. We'll choose Straight Talk here, only because they don't require you to use auto pay to lower your bill to $45 a month. It's $45 a month from the start and you get unlimited talk, text, and 2.5GB of 3G data with throttling after that. A runner up here is Page Plus Cellular, a very popular MVNO but it is more expensive at $55 a month for essentially the same service as Straight Talk and Net 10.
Lastly, whether or not you agree with the choices listed here, for the best overall deals, we recommend AT&T based MVNO's. AT&T MVNO's currently offer the best overall coverage maps and come with LTE data speeds.