Week 1 is always filled with with insanity. Expect the unexpected. Everyone is throwing in the towel for Larry Johnson, so he just might be the best start here.
It is possible that Derrick Ward might barely see the field. He might not even be the #2 back by the time game 1 rolls around.
As for Stewart, you have to watch and see if he is even going to be active for week 1. If he does play, it likely won't be much.
The remaining option is Larry Johnson. Going up against a tough defense, but one that has seen changes to personnel and coaching over the offseason. Still a tough defense, but Johnson is a tough runner when healthy and dedicated.
Still a few days till lineups are due, but if I gotta pick right now, I am picking Larry Johnson.