I hate the NML regen. That said, the items pay extremely well. I don't think haunting can be beat for gold/hour though, at least not at my size. My smaller alt does very well on NML though. Didn't read all the responses so apologies if this has been answered but the variation your seeing in haunt plunder is likely due to T5 upgrades allowing larger clans to complete it with fewer actions.
If you are active nearly 24/7 and are in a clan that completes haunts in 1 hour and hit items every time, haunt is by far the best. The reason plunder is going down is because while bigger stats are doing more damage, the plunder isnt increasing in a direct relationship, as it increases far little in conparision to the damage.
Personally, I make the same if not more from longer haunts. 1 hour haunts have 2-3 second item phases. I don't get the appeal.
If you can hit hauntings without pots its the most. Attack builds that can't hit haunting should stick to No Mans Land. Hansels should hit either ambush becuase if the stealing phase or hauntings becuase of the item phase.