In Avowed's "Fires in the Mine" side quest, the decision to stop or support Darle impacts rewards significantly. 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 is the superior choice. You receive 1091 XP (212 XP for the kill + 879 XP for debriefing), 900 gold 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 additional gold and crafting material significantly outweigh the slightly higher XP from supporting Darle. Furthermore, this choice maintains a positive relationship between the Aedyrans and Thirdborn.
From a gameplay perspective, stopping and killing Darle provides the best combination of XP, gold, valuable loot, and positive narrative consequences. Therefore, preventing the mine explosion is the recommended course of action.