Such a hard question to answer because that can mean so many things. Some films are powerful, some influential, some are just plain fun. A film that wins lots of Academy Awards may not be hugely enjoyable to watch and your best 90 movie minutes of the year may be for something you’d rather not admit.
The Conduit maintains that Airplane (1980) should be a starting point for any such discussion. It clearly is not filled with actors baring their souls, nor contains a score that makes the heart race, but it is a remarkable achievement. The sheer volume of jokes, carefully layered into every scene, is astonishing. Repeated watching is tolerated because new audio and visual humour is spotted every time. The film also created a new style of parody movie and even cast a belovèd character actor in an unexpected comedy role, giving us the genius that was Leslie Nielsen.
Quite probably the most valuable thing to take away from any question such as this though is that everyone has an opinion and theirs may differ very strongly from your own. That is cause for celebration and a starting point for a discussion, not a reason for insult or mockery.