I think it's
Gandhi.
Try lists like these:
Which movie is your favourite?
www.timeout.com
Every decade since 1992, Sight and Sound has complemented its celebrated critics’ poll by formally sounding out the world’s leading directors on the ten films they believe to be the greatest of all time. Though it has always been global and inclusive in scope, the poll has expanded...
www.bfi.org.uk
There are over half-a-million features listed in IMDB, and excluding short fims and TV shows.
Assuming that you can watch one new movie ("new" means something you haven't seen, even if it's old) every week for the next fifty years, and around 50 weeks a year (given a two-week break per annum), you would be able to watch only around 2,500 films.
Presumably, you would watch a movie because it's great, then for the next six days rewatch it or parts of it and then write and think about what you saw, then do the same for the next film the following week. Also, the selection would represent different countries, decades, and even genres.
One might be tempted to select based on one's preferences, but keep in mind that preferences are ultimately based on range of choice. For many directors, critics, etc., such choices might involve having seen thousands of movies vs. average viewers who will only get to watch around a new movie a month. Hence, the two lists above.
Finally, the same might apply to books, music, etc.