Baddy Kills
 

How are the drops like Chests and Maps picked? Does the person that deals the most damage get the drop or is it the person that strikes the last hit?

Most damage = reward owner.

Thanks you! could you also possibly tell me which baddies drop the maps? I've seen pyrats and bandits drop them so far.

I would say Bandits are better to farm off of because there aren't as many people trying to kill them. Pyrates are also efficient. Each have their pros and cons.

Bandits
Pros: Less people, located in a secret area that can only be made accessible by a draisine, so not too many new players are there.
Cons: Less bandits means more people fighting over a single bandit. Try to 'claim' a spot.

Pyrates
Pros: More pyrates, can also do the pyrate quest and gain 1k gralats while you do it.
Cons: More people, meaning even more people are fighting over a single pyrate.