John Wayne + Lee Marvin
I love James Cagney, but he was miscast. Dan Dailey was also miscast.
If John Wayne had played Flagg and Lee Marvin Sgt. Quirt, it would have been a classic. Wayne and Marvin did a number of John Ford movies; I wonder why Ford didn't use these guys?
If Marvin had not been available, Forrest Tucker would have also made a great Quirt.