Cutler, no doubt. Regardless of how McNabb and co have played recently, they're going against the number five overall D, and the number three passing D. The Redskins offense is what's killing them, not their D. Don't get that confused, because it will come back to haunt you. Not all good defenses translate to good fantasy D's, so don't let that fool you either.
On the other hand, Cutler has a fantastic MU against a team that has been awful against the pass, and just lost their top pass rusher. To me, there is no question who should start this week. Cutler all the way.