I'd lean toward Foster.
You never know what will happen between now and week 5, but with the Smith injury and Carolina's hideous OLine play Monday, there's a chance the Panthers will want a speedy back who can catch the ball - and that ain't Davis. Even if Foster doesn't take the starting job outright (and Davis would probably get goal-line calls even then), he should see an expanded role.
I want to die peacefully in my sleep, like my grandfather.
Not screaming, like the passengers in his car.