I would pick Rose over Westbrook simply because Rose is still the better go-to guy. The guy I'd rather see with the ball in his hands in the 4th, especially with the team down a bunch.
That's like saying Dirk is better at speaking German than Westbrook. Seeing that Westbrook hasn't had time (or the need) to learn, who's to say he wouldn't be kicking Dirk's ass at German Scrabble in two weeks? ;) Westbrook has never been a go-to guy, not even at UCLA, but I think he'd be just as good or better than Rose in that role if he had to be that guy for an extended period of time. He's already a better shooter than Rose, just as good of a finisher, and a better free throw shooter.