I don't do any math, but since I'm still a low level player I try to space out my options. I'll gather alumen, black alumen, silver ore, eff water, electrum ore, cobalt ore, and some shards. That way I have a wide variety without it being too overbearing.
Again, I don't really do the math behind it. I just make enough to feel content. I actually end up giving away probably 60% of what I make to fellow Free Company members.