I wish I could be a lot more accurate about this, but...
Movies: I know I did a lot of repeat viewings during the 1970s of Citizen Kane, 2001, The Exorcist, West Side Story, Roger Corman's Poe films, and any number of Hitchcock films, so some segment of that group has to account for my highest numbers. Hitchcock just might be the winner there, but narrowing down which of several films would be nearly impossible.
Musicals and plays: The unfortunate thing is that for a number of years I neglected to take proper care of a lot of my programs, and those would have gone a long way in answering this question. Plays, I really have no idea if one or more have been revisited enough to count. For musicals, West Side Story would have to be at or near the top of the list. Other contenders are probably The Music Man, South Pacific, maybe another R&H or two. I'd like to think there has been more variety when it comes to repeats, but I'm at a loss to come up with it.