NFL Week 15, can only start 2 RB and have S.Jackson, J.Charles, R.Mendenhall, D. Williams. Please Help!?

I need a big week as I am up against Peterson and Brees... Had Manning and Wayne so I am off to a good start but now I need to decide which two RB to use and I am stuck... My gut says Jackson and Charles but a lot of people like Mendenhall. Any help?