Maptools, for me at least, has the lowest 'buy in' compared to what you get out of it in return.
Fantasy Grounds II is weirdly complex and not in a good way. I still haven't managed to figure out how to build modules with it despite owning it for a couple of years now. In comparison, I run and play in several Maptools games.
Maptools also has a much more active community than FGII. It is also getting improved on all the time and the next version number (current version is 1.3 beta) will see a massive improvement in performance and functionality as it will be javascript scriptable.
For a program that is free, Maptools gives unbeatable value for money. FGII leaves a lot to be desired and quite frankly pulls up behind Maptools even without the price consideration. For a product you have to pay for, FGII just doesn't stack up.