FF4 for nostalgia.

FF12 for open-ended adventuring, License board, lore, providing a challenge to shake my confidence when side exploring making me feel the need to overcome said challenge, and having an offline FFXI feel using the same engine, but with AI party members. Though curious about Zodiac/International edition's revision of the License board.

FF13 for challenging battles during the entire duration of the game, never making me feel like I overleveled, role system (whole different difficulty if you set the battle to Abilities for default action and manually choose instead of Auto).