It's a tossup, more a matter of personal taste.
Problem is there are very few shots in circulation of Sergio in his best shape in '72, so Arnold has a huge edge in perception given the number of widely available pics of him. Big advantage.
IMO Sergio in '72 was Arnold's motivation or fear for getting in his best shape in '73-'74. He expected Sergio to compete those years, particularly following the Mr. International situation.