I just picked up Shonn Greene, but I may drop him for Jamaal Charles. Good idea?

Sure, Greene had a lot of touches against a horrible Oakland, but Jones is getting TONS of touches (and doing well with them). Larry Johnsons has been sucking all year, and now that he's out for a week, I could put in Charles and hopefully he'll be the starter from here on out (he does have a better yard avg.). Should I do it, or stick with Greene. Will any of these two produce points? Which one more than the other? Tx!