In Avowed's "Fires in the Mine" side quest, the decision to stop or support Darle significantly impacts rewards. While both choices offer XP, preventing Darle's mine explosion yields superior overall rewards.
Supporting Darle: This nets 1026 XP. However, it eliminates monetary rewards and further strains relations between Aedyrans and Thirdborn. Lying about your actions doesn't alter the outcome.
Stopping Darle: This proves the more lucrative option. You receive 1091 XP (212 XP for the kill + 879 XP for debriefing), surpassing the reward for supporting him. Additionally, you gain 900 coins from Seynon and Kada, and loot from Darle's corpse: a Blackwood Branch (a superb upgrade material), Wild Mushroom Stew, and two Beetle Pies. The food items are less significant, but the Blackwood Branch is a valuable addition. Furthermore, this choice maintains positive relations between the Aedyrans and Thirdborn.
In conclusion, while supporting Darle offers a decent XP reward, stopping and killing him provides significantly more XP, substantial coin rewards, valuable loot, and a more positive narrative outcome. Therefore, stopping Darle is the optimal choice for maximizing rewards in "Fires in the Mine."