FFVI-- Easily my favorite. While the gameplay wasn't what it could be, it made a good start of things to come gameplay wise. What really made it shine was the fantastic character development (best I've ever seen in a game), good story, incredibly music, and the best villain ever.
FFIV-- Really not a great game by todays standards, but I mainly like it for nostalgic reasons.
FFXI-- Oh yeah, I went there and put this game on my list. It may be unconventional but it is a great MMO (read: different from WoW). The crafting system was tedious but pretty nice, there is a good amount of early and mid game content and a lot of end game content, the community is great, and I love love love love the job/subjob system. Also, I was one of the few people that seemed to actually like Balista. :-p
FFVII-- I really didn't like this one the first time through, the graphics just disgusted me. If a technology is there but it's just doesn't look that great yet, just don't use it. True, it was good for the time but that doesn't mean it didn't look like ass. Other than that, it had an interesting story was fun. It definitely improved on gameplay where FFVI was lacking.
FFI-- Another game that makes it on my list for nostalgic purposes. It really doesn't hold up to todays standards and it isn't that fun. I like it mainly for the memories (though it was the 2nd FF game I played with IV being the first).
FFIX-- After the abomination that was VIII and the tech direction that VII took, this one was a welcome change. All in all, it was a good game; too bad it completely fell apart in the very end.
FFX-- It was a decent game, the gameplay wasn't great, the sphere grid sucked, and the story was beyond predictable. This game got an overwhelming meh.
FFXII-- The graphics in this game were beautiful. The writing was good. THe story wasn't bad. The gameplay was great. The world felt alive. Even the voice acting was incredibly high quality. Even with all that, I just didn't like the game. I don't know if it was because the story was so political or the license system was just silly (in that every character turned out to be the same-- wya to take the worst part of FFVI) but I just couldn't get myself into this game. I tried several times and each time I eventually just got very bored with the story and couldn't bring myself to progress any farther.
FFIII-- I just didn't care for this much. I played the DS version and it didn't appeal to me. Improving the graphics really didn't do anything to hold the game up to todays standards in a game. The job system was fun and a good start for other games, but it just wasn't that good.
FFVIII-- I actually prefer FFX-2 to this abomination. The story was beyond pathetic, the draw system was just irritating, the characters had absolutely no life at all and were very 2D, and, well, the game is just bad. I know I'll catch some criticism for this, but I expect FFXIII to measure up to this game.