FFVI: I think it's a very good game, but I don't consider it "best of all time" quality.

FFVII: See above. It's an entertaining game for very different reasons than FFVI, but it has terrible writing after disc 1 and has what feels like a half-finished plot. I still like it a lot, but it's not close to among the best.

FFX: Unlike the first two listed, I just didn't like this game much at all. Linear, cramped gameplay combined with annoying characters just makes it not an enjoyable experience.

(I would say FFIX, but I actually don't think the game is nearly as hyped anywhere else except EoFF )

Xenogears: I was never really able to get into this game, though I've been meaning for years to give it another try.