Dungeon Divers pts per energy for Stage 10 Hard Mode
Assuming the numbers that HH posted are correct - you'll get on average 0.682 points per energy on stage 10 hard mode. For comparison, stage 25 gives 0.6413, so you get more from stage 10. However, stage 24 gives 0.7053, while stage 20 gives 0.7602.
So - 20 is still the best bang for your buck, in terms of DD points and quality of gear. Hard mode stage 10 I think would be the second best option, over stage 24, since the slightly lower points per energy is outweighed by the better quality of rewards.