Pinab all the Haunter
With lick being added to the moveset of Gengar on that raid day, and there being 4 pokemon its going to tear into in gen 4, being able to mass farm candy from all the wild haunter in this event so mass gastly catching later wont be a stupid tedious grind, plus 20 gastly candy per catch on raid day at minimum is going to be fantastic.
Answers
Only about 900 in my bag, but I agree, all my pinaps are going into Duskull and Shuppet. I've been getting 8-10 rare candies per day from that research task.
edit: I went out for a couple hours tonight, mainly to spin stops and farm rare candy, and I got a bunch more of the evolve Duskull/Shuppet rare candy tasks, to bring my total harvest for the day to 23 rare candies from field research alone. That is huge for a free player who doesn't plan on spending any green passes on Giratina.