In the case of Mighty and Toova, they can end the mobs in 1x AOE with Aqua and Rock Spread respectively at high enough MATK (380+?) as well so you can grind around longer.Chronos' Umbra Memory RoomThe mobs here always spawn in 3s without fail and always gives 12885 EXP after battle. While all the current 5.s at Max level and L48 weapons minimum (L60 Rank 3 for Anabel) can end the mobs in 1x strongest AOE attack. And most maxed level 4.s with AOE and L48 weapons minimum can end the mobs in 2x strongest AOE attacks.

So lets go through some other factors between the 2, assuming you all restore HP/MP via warping to Promised Fruit Pot at Rift of Time:Beast King's Castle 1F/2FMobs are L44 to 45 and give 10208 EXP to 14386 EXP per battle depending on the lineup. Your luck may vary on what spawns for battle but based on numbers alone it loses out to Chronos' Umbra Memory Room, which always gives 12885 EXP per battle.Well if only life was that simple.

So 100 battles should suffice and I got the average of EXP.

Another eden chronos umbra walkthrough