Of publicity and things it definatley goes to Ali Frazier 1 that fight was advertised like crazy Importance Louis Schmelling 2
Cribb Molineux II received more coverage in the contemporary press, than the battle of Trafalgar! This is not something new!
Ali-Frazier 1 was the biggest fight ever. It garnered the most acclaim and actually lived up to the hype. Louis beating an old Schmeling takes a back seat to it. Non heavyweight superfights like Duran-Leonard or Hagler-Hearns also fall behind.
I think in purely boxing terms Ai v Frazier 1. Overall though I'd have it at No.3 behind Louis v Schmelling 2 and Johnson v Jeffries because of the political and cultural angles of the other two.
The only acceptable answers imo are Louis/Schemling, Ali/Frazier 1 and my no. 1 pick would be Johnson/Jeffries