I think Haas has a better chance of taking Fed out....He posseses what, in my opinion is the one weapon that is essentila to having a chance of taking out the Rog : A consistent and deadly Down-the-Line backhand. In fact, I'd say he's probably one of the few guys on tour that I would rate as having overall, a better backhand than Roger. Safin, Nalby, Nadal (well his DTL BH is his forehand vs. Roger), Gasquet, Berdych....the one thing that all these guys have in common is that they have backhands that are good enough to break down Fed's, and in particular can rip DTL backhands either for winners or to control points. Kiefer can hit it OK, but Haas is one of the best in the business at it....and it shows, since he's done relatively well against him in the past.
But I'd agree that Kiefer is probably the only guy left that stands a chance...he's troubled Rog in the past as well.