II is the black sheep, but III is definitely the most under-appreciated. It kind of bums me out, but I totally understand it. That being said, III is one of my favorites for some reason. In my opinion it was the title where Final Fantasy truly found its identity: it began the great job system (I don't count FFI since you merely choose at the start and that's it), introduced some of the greatest jobs still to this day, introduced summons, started moogles, etc. Also, I absolutely love the soundtrack and the oldschool feel to it, and when you really think about it, the fact that they were able to make the enemy sprites in the NES version look as good as they did was just insane.