I actually like a QB/RB combo, as long as they're top-drawer options. Two years ago I had Brooks/Deuce, which was great until the Saints embarked on their annual mid-November fade, then last year I had Hasselbeck/Alexander, which was even better.
That combo covers you whether the team has a big day running or passing, without the blanking you get from a QB/WR shutout. I don't have the same experience with RB/WR, but you should be fine with the Chad/Rudi pairing, for similar reasons.
One qualifier: I certainly wouldn't turn down Culpepper/Moss or Manning/Harrison in any format, and if you're in a points league instead of head-to-head, the QB/WR combo is a much better proposition.
I want to die peacefully in my sleep, like my grandfather.
Not screaming, like the passengers in his car.