In evaluating you guys instead of you guys evaluating them guys I would say the best answer to the OP's question, given so far, is . . .
It is a close one between between Greb-Tunney and Norton -Ali
When talk of Harry Greb arises we also often mention Greb-Walker (I think there is a thread running on that fight right now) -- with Norton, on the other hand, his only other go to story is getting mangled by Foreman, otherwise he gets no love.
So, best answer to the OP's question so far . . . (wait for it) . . . Norton-Ali I
Continue answering I will soon pass by this way and once again pass judgement on you all. -- You're Welcome!
P.S. Small Spanish guys who's names begin with Z don't get much mention, even here (unfairly so); so it's hard to judge a fighter's defining moment when so few people speak of you to begin with.