premise: There are traditional cowboys and tough guys on the list, but the former (as in Stagecoach , 1939, and The Searchers , 1956) is limited mostly to John Wayne, and the latter (as in The Maltese Falcon , 1941) to Humphrey Bogart; and you get the sense these films were chosen more out of nostalgia for their stars than for their dramatic power.
hypothesis: John Wayne's favorite film he acted in was The Searchers.