As a console-only gamer in the 90's, the SNES and PSX Squaresoft games are among my all time favorites. The nostalgia runs strong for me. I recently played through the Steam versions of FF6, 7 and 9 and had a blast doing so. FF7 in particular was incredible, I didn't like it that much on release but 20 years have apparently changed my mind, it's the best game in the series by far. Masterpiece is the word that comes to mind, flawed but still excellent.
FF6 is fun but it's a different type of game, it's old school and the story is much simpler. Characters have little to say and everything is to the point, the later PSX FF's have more conversational dialog and better fleshed out stories/characters. FF6 is fun and it's a quick game, but not the best in the series as I had previously thought.
FF9 - great game. Fixes all the technical and gameplay related flaws of FF7. Great combat, mobs can and will KO your characters, fast paced fights on pc with battle speed cranked... and four controllable characters (yes!) instead of three. Epic cutscenes. Great progression system, plenty of great characters and memorable moments. But ultimately it never takes itself seriously enough to match FF7. FF7 was dark, and gritty, and the characters had real issues they were battling. FF9 sort of won't commit all the way, it keeps things light-hearted the whole way through. Which I remember being welcome after the depressing garbage that was FF8 (Squall sucks). But Zidane is happy-go-lucky all the way through, Quina is a walking punch-line, Steiner is clueless, Eiko is Eiko...etc. I like all these characters but they're all never more than semi-serious throughout. The music is cheery, almost to a fault. It's never really possible to invest in the characters or the impending doom the world is seemingly facing like you could in FF7. Ultimately that means it can't touch FF7 for me, which is fine and not really a complaint. FF9 also has a laughable final boss sequence... oh hey, let's introduce a new "ultimate bad guy" we've never seen or heard of for the last battle, folks love that!
But faults aside, FF9 is still really fun and I enjoyed the hell out of the trip down memory lane. It's up there for second best, I stopped playing the series after FFX and neither that nor FF8 is going to beat FF9 for second place. I doubt I'll play FF8 again simply because of Squall, so that leaves FF4 as the last one left to replay I guess. Looking forward to it whenever I get around to it.