For me it was chickens in the last game I played. It took me about a year to have 200 chickens but when you have so many outside, attackers will target them before colonist or turrets. Not a very smart use of triple rocket launchers by the attackers... Chicken population grows extremely fast, when I sold every chicken I got something like 5000 for all of them. It required a minimal amount of labor and investment for such a huge return in a short time.
I mentioned before some issues with infestations. I think bugs should attack doors in order to kill colonists, now you can shoot, then hide behind a door and repeat until they are dead.
I mentioned before some issues with infestations. I think bugs should attack doors in order to kill colonists, now you can shoot, then hide behind a door and repeat until they are dead.