TBH, I haven't really thought much about the particular effects of factory resources. My goal is usually to slot the most at one time, so if I have 5 oranges and 5 slots, in they go. I agree that coffee is a strong one and quinine is great for healing in wartime. But if I can fill up a city with cotton, kaolin, or chocolate, I focus on filling the city. The Economic legacy is a total, so getting as many slotted as early as possible is my objective.