I am going to be starting with IX because thats one i haven't played yet but been meaning to for years. Well, i did start it once but didn't get very far, now i am trying again with the hd remaster.
My favorite is VIII, is the one i have played the most, i don't really care about the hate it gets, people autistically hating the junction system is trite as fuck. I wasn't into the card game though so i missed a lot of the stuff that would make for OP builds, the system gives you ways were you can break it but i don't care too much about maxing and the meta when i play games so i played very normally and still beat it without really feeling frustated about the junctions. I feel that became the main opinions thanks to youtubers who didn't bother even giving it a thought, like sure, the summon animations take too long but if you are junctioning properly theres no reason why you should be summoning so often or barely at all for most fights, if you are junctioning decently theres also no reason to grind, so thats cool. I'll admit the orphanage plot point and the amnesia was kinda silly.
Gameplay wise i feel X was the most fun one, i really enjoyed it too, probably my second favorite.
VI was nice as far as snes games go but i still find it extremely overrated, a remake of VI would be cool for the aesthetic alone though. VII was ok, i feel some of the lore and concepts were more interesting than the game, Midgard was a cool setting to have any sort of fantasy story in, but i found myself bored often playing it. I don't very much care for classic FF, 1-3 i played briefly and found them very arcaic and tedious (i was already above age when i emulated them) i didn't beat V and IV either, i droped them at like a quarter of the game in.
XV felt unfinished, it felt a lot more like westerner rpg and it had the same tone inconsistencies western open world rpgs have sometimes (this just in, your father the king died, the kingdom is in disarray but hey, its cool, lets go fishing and sightseeing just after hanging up! ) i usually don't go for that type of open world games but i had a nice time with it regardless, it was a pretty weak game as far as combat goes, and the few dungeons really sucked but the character interactions and just chill road trip roleplay made up for it. The plot was not great but i did liked the characters so that was cool, just needed better dramatic climaxes, the random dialogues with character exposition you have with each companion while traveling are more memorable than the mayor events in the main storyline.