McEnroe v Borg?
Argentina v Brazil?
Celtic v Rangers?
India v Pakistan?
In that thread about baseball I recommended to Morethanjustadad a book called A Tale of Two Cities.
The introduction describes the New York Yankees vs the Boston Red Sox as "the most famous rivalry in sports".
Clearly it isn't -- only a few countries follow baseball, so it's hardly famous, really.
But what is the greatest rivalry in sport, worldwide?