I would say Powell, if he resigned instead of making the case he didn't believe in at the UN. He put his stamp of approval on this war. I think it was a lapse in character. He has a soldier mindset in a civilian position. I really like the guy, and his thinking was right on. Powell Doctrine, pottery-barn rule, etc was all right. But when it came down to it he didn't stick to his guns.
I think Clinton would be a great SoS, but I am worried for his health. Clinton is one of the most popular Americans around the world, and the guy can communicate and win people over.