Running back issue?

i have a tough decision to make week 16. I am in the semis and have 4 solid runningbacks. Steven Jackson who has the tough pittsburg defense but is the only back on the team. Willis Mcgahee who is also the only back and has seatle. I also have Jones-Drew who splits time but is running against a weak oakland team and rudi johnson who is also splitting carries but is running against a weak clevland team in a game that should be high scoring. I cannot decide which two to start. Choose two and explain why,