Fantasy Football Flex help!?

I have Cedric Benson riding the bench. So I have Jonathan Stewart Vs AZ, MJD, and Ryan Torain Vs. Dallas slotted in at the moment. Should I sub out one of these backs for Derrick Mason Vs. NO on the flex? And what QB to start.. Ryan Fitzy Vs. MIA or David Garrard Vs. IND? I'm thinkin Garrard but he might not start.. Thank you for your help in advance!!