Which is the BEST ( least expensive, both hardware if needed, month to month, w/ unlimited data, wireless mifi????

It depends greatly on what city and country you live in and then you would need to get lucky and someone happen to see this post that lives there.
Your best bet is to search the providers you know service the area you live and see what they offer.

Still you will likely never find a unlimited mobile broadband package that allows you to run a computer off a hotspot or tethered. There are plans that allow so called unlimited on phones themselves but this is only for the device and even then many of the plans have fine print that makes them not really unlimited.