I voted for FF2. I think the settings are the coolest, and the story is the best. It's fantasy with a little but not too much technology, which is what bugged me a lot about the ther ones.
Land of Monsters is the fucking coolest shit ever... it's also the best because it had a lot of pioneering FF stuff in it that shows up in the later games- it was the first game to have calling, and it really implemented well the concept of 'using' weapons which would have a special effect, but you weren't really sure what that effect was until you experimented a lot.
The secret, uncatalogued stuff in that game is really well-done, and the end boss isn't ridiculously stupid the way, say , Sephiroth is.
Although I do agree that the spells in the later ones are more fun to watch.