In the eternal Charlie Chaplin vs. Buster Keaton debate (for a lively version see 'The Dreamers'), Keaton was ahead on points after seeing 'The General' - possibly the most elegant and awe-inspiring silent film ever made. But Chaplin's 'Modern Times' came very close for its satirical brilliance of man wrestling with a mechanical world.
Then there's 'Limelight', which sort of solves the debate by being the only film ever to join the two comedians on screen, in an extended musical slapstick that is one of the film's highlights.
One of Chaplin's last films, and a 'talkie', 'Limelight' (1952) is a nostalgic and autobiographical melodrama. The story tells of a once-famous clown, Calvero, passing on the torch to a younger generation. Alcoholic and on the decline, Calvero guides a destitute and despairing young ballerina (Claire Bloom) back to dancing and a triumphant career.
Underneath is the tragedy of Calvero - i.e. silent comedy - getting old and outdated. (Ironically, the sharp and witty dialogue is what keeps the film interesting in many places.) At a benefit evening, Calvero makes one final stage performance, and this is where the memorable scene between Chaplin and Keaton takes place. With only a piano and a violin, and much ensuing havoc, they create a fitting monument for the silent comedy they both perfected...
...even if Chaplin was rumored to have cut out the best parts of the scene, which were Keaton's. So maybe it doesn't quite solve the debate after all.