Whichever is your favorite.
Quite honestly, as a filmmaker and someone who's poured a lot of time into studying the classics, my actual favorites are often quite random (and Citizen Kane is certainly not among them). All the technical merits of a film only amount to so much. Whether or not you were affected, moved, entertained, amused, frightened, whatever, by a film is really the only criteria.
Now when it comes to FAVORITES, probably the Third Man or Lawrence of Arabia.