Personally 8 is my favorite as well it was also the first FF I ever played back then after that picked up 7,9, and up till today 7,8,9 are the only ones I actually finished and did most of the side quests with. And they are by far my most favorites.
Also played 6 but I never was able to finish that one story was oke tho.
10 is also one of the few I finished but besides the updated graphics it felt pretty meh to me.
12 tried but failed to hold my attention. 13 was a lost cause to me I started it but not even an half hour after I landed on pulse I shut the game of and never touched it again >_> attempted again with 13-2 because it had monster taming but it snuffed out pretty fast. Might try 13-3 (seeing it has hart of kingdom like combat) but seeing the story doesn't really pull me in I might just wait for 15 XD.
But I do hope more tibits get implemented in 14ARR that relate to the older ff's like 7,8 or even 9 (would be awesome to see a fate or event with those ff9 white dragons for example)