User blog comment:Leenakeenev/Best Quests to gain as much EXP as possible/@comment-2061246-20160829224032

In theory, the best EXP/time is the Bariura:Bonus stage.

It has terrible EXP/Energy, but with Omni units and pingu status, you can quickly grind through the level without trouble at 15k EXP per run, or 30k EXP during the 2x EXP Event.