Tie between FF7 and FF8.. FF7 because of materia leveling and chocobo breeding, FF8 because I loved the game so much I kept starting over to do everything perfectly. OCD.

I think overall it was longer before I beat FF8 though, I did every side quest, leveled everybody up completely, got every GF ability I could, got all the cards, got 100 of all the spells for my main characters' junctions.. I ended up beating Ultimecia with absolutely posotively no problem, even with my characters being shuffled about.