Its fourth down. 30 seconds left. You need a touchdown to take the lead. What would you choose? A great coach, or a great QB?
I would pick a great coach. Its not an easy choice either because they both play very important rolls. The QB see's when an audible needs to be put in place. The coach calls the plays, makes the plays, and see's which players are fit for each play.
Plus a great coach can mold the QB into a great player. Who will mold the coach? If you have a great coach and a not so great QB, you can run the ball.