Okay - so a similar outcome to the dungeon divers events. Hard10 gives 0.952 points per energy, vs Normal25 giving 0.9174, Normal24 giving 1.0135, and Normal20 giving 1.1132.

In other words, 20 is still optimal for points. In this case though I'd probably argue that 24 is the best approach for tournaments, if you're able to farm it efficiently and quickly.

Personally I'll be doing 20 when champ training is active, so I can solofarm food, and Hard10 when it is not.