For me it's Billy Wilder and George Stevens. Although I am a big Hitchcock fan, I love Wilder and Stevens for the both the length and breadth of their careers. They could direct classics in various genres like musicals, comedies and dramas and I also like that Wilder was also a writer. As good as Astaire & Rogers were I, like many, feel their best or one of their best films was Swing Time directed by Stevens, who could also direct Giant, A Place in the Sun, Diary of Anne Frank. I also admire Elia Kazan with classics like Streetcar and On the Waterfront. When there's a movie I can watch a million times and never get tired of it for me that is a classic which stands the test of time.