NES:

Best: FF I

Overall, I have a hard time going back and playing the NES era final Fantasies (Not sure why, as I have no trouble with some other NES games like Legend of the Ghost Lion or Mother 3 which I didn't play until the PS3 era of games was already a thing), but this is by far the easiest one to get into.

Worst: Final Fantasy II

Enough people have ripped into this one.


SNES Era

Best: Final Fantasy VI

One of my favorite games of all time. Amazing cast, fun battle system, the split party sections were fantastic and I wish more games did that, and the Villain was outstanding.

Worst: Final Fantasy Mystic Quest..... okay Fine FF V because of your dirty rules.

Seriously though, FF V is great. Best overall generation for Final Fantasy. Even Mystic quest is at least playable and has some good things going for it.

PSX:

Best: FF IX

The Call backs and nostalgia are all great, paired with a fantastic sound track. That asside, despite the slower gameplay early on, the battle system is quite fun, the best mini games of the series, and a damn impressive cast (Even if a couple characters get a bit shafted).

Worst: FF VIII

I think I've bitched enough.

PS2 era was mostly Unimpressive for me, but X was easily the worst, second worst entry in the whole series. And despite some good premises, XII was badly executed for a variety of reasons. FF XI gets the nod because while I'm not a big MMO guy, it was at least fun.

PS3.... let's not get into that generation.