McNabb is the obvious choice here, and I guess that's why you came here seeking opinions to make sure this is the correct choice. It really comes down to match-ups, specifically Philly's passing game vs OAK's defense in general --- which outside of their season-opener, has been dreadful. McNabb SHOULD shred OAK's defense at first glance.
Now, Schaub LOOKS attractive, since the Bengals give up an average of 230 yards to opposing Qbs, and we can all agree that Schaub is ABOVE average, but just know that Cincinatti has employed "bracket-coverage" effectively taking away opposing offenses' best WR. this is relevant bc if Schaub is to have a great day, you would think that AJ would be a big part of that equation. So the question remains, if you decide to go against the grain by sitting McNabb bc you believe this game will be a cake-walk where the Iggles will attempt to regain continuity on the ground in the 2ndH, will this tactic be at the EXPENSE of their passing game...?
I would just not overthink this decision and start McNabb and hope that OAK puts up a good fight for at least 3 qtrs, that way the Eagles will be forced to be two-dimensional, balancing the run and the pass.