I actually had a 3ish month break at one point between when FATE farming was the main method of levelling and when dungeon XP was boosted. I'd have to also vote for doing dungeons over FATEs. I've actually levelled twice in one dungeon run once or twice, likely in Haukke Manor around level 28 (when it unlocks), doing a full run killing every monster in the dungeon for XP and eating food, having a rested bonus on my full XP bar, and having the FC XP boost buff.