Ummm, the list of favorite Hoffman/Dunaway films is a short one. Little Big Man is the only movie in which they both played a large role. They both were in 1999's The Messenger, but in smaller roles. I am not sure they were even on screen at the same time.
Now, it is possible you are saying Little Big Man is your favorite movie in which either Hoffman or Dunaway appear. Though that would mean you like it more than: Chinatown, Network, Bonnie and Clyde, The Three Musketeeers (the 1973 version with Oliver Reed, Raquel Welch, Richard Chamberlain), Mommie Dearest, Tootsie, Kramer vs. Kramer, Rain Man, Marathon Man, All the President's Men, Papillon, Midnight Cowboy, and The Graduate.
-Jason "you are certainly entitled to your opinion -- but Hoffman and Dunaway have some darn impressive credits to their names" Evans