@ant-heuser-kush OoS was fun, but you fight wave after waves of skeletons only to finally fight the bosses and you get one of 4 skulls (foul, disgraced, hateful and villainous), which don't seem like they pay off as good as chests or merchant stuff. Then there are the forts, which still you fight waves of skeletons only to get 1 stronghold which is like 3 villainous. The skeleton ships are the best cause you can get 4 skeleton captain skulls which are like 2 villainous, but still fight wave after wave. Plus forts and ships, everyone else is also competing in getting them too, so it can take longer if you fight others for the loot.
Really, merchant alliance is best pay out, but you have to complete the task and can be boring a bit, but bright side is not too many people go after merchant workers, which is why I like doing them alone.
Gold Hoarders, there are so many types of chests and relics you can find all over the place, I have barely worked on this and yet it is my second highest factor. Honestly, you need to work on this but not as hard as the others.
I've spent countless hours sailing to islands, and the worst ones were the big islands where it took forever to find the skeletons not to mention once you found them, other factors could easily delay you (no water or ammo around and you're fighting gold skeletons that all have pistol that can hit you from miles away 100% accuracy, raining and you gave a swarm of plant skeletons that keep regenerating health, night time and shadow skeletons...etc...). Honestly, I really feel that there needs to either be a bigger reward for the skulls you cash in or more variety in skulls cause OoS took forever for me, and I've heard others say the same thing.
Still it is a fun factor, but it doesn't pay as good as the others...