I have only played 7, 9, 12, 13 and 15. I reached around level 20-25 in FF 14, but that isn’t even halfway into base game, so not counting that. I dropped it because of the huge time sink it is.
As for older ones, while I don’t mind retro games, they feel a bit too retro. How would you say those older games are, if you don’t have any nostalgia for it?