Who is the greatest?

It was January 20, 1970 and The "SuperFight - Ali vs. Marciano" was shown one time in 1500 cinemas across Europe and North America. Afterwards, all prints of the fight were destroyed, except one copy given to the U.S. Copyright Office. Other than one showing on ABC's Wide World of Sports in the early 70s, it has not been seen since. Marciano, the only Heavyweight Champion to retire undefeated, was 45 in 1969 and missed the challenge and glory of the ring. Ali, 27 and, at the time, undefeated as well, had been stripped of his title and boxing license for defying military induction.Both champs were motivated to determine, once and for all, who was the Greatest Heavyweight Champion of All Time!