It really depends on how you define the term 'greatest' Here's a definition: greatest \greatest\ adjective [superl. of {great}.] 1. not to be surpassed. 2. largest in size of those under consideration. Syn: biggest, largest. 3. most of. 4. highest in importance or degree or significance or achievement; most eminent; 5. highest in quality.
Applying this criteria: 1. not to be surpassed - Corrales v Castillo 2. largest in size of those under consideration - Ali v Frazier I Syn: biggest, largest. 3. most of - De La Hoya v Mayweather (2.4m PPV buys) 4. highest in importance or degree or significance or achievement; most eminent; - Jeffries v Johnson (for significance) 5. highest in quality - Leonard v Duran
and thriller in manilla.......... johnny tapia vs paulie ayala mike ayala vs danny lopez (re-watched that recently and its superb with some crazy drama- fight ends......then carries on again!) obviously, barrera v morales.....