What is the greatest movie of all time?

Determining the greatest movie of all time would depend on defining what is meant by "greatest". Opinions on what makes a movie "great" would be completely subjective and vary from person to person. Those opinions may be based on how funny, interesting or exciting a given movie is to a person, which in itself is also subject to individual preferences and personality. Some people might even base the criteria on achievements such as number of Oscars awards won, biggest box office record or popularity achieved. There's no way to answer this question in a definitive fashion.