The absolute best condition Sergio got in to was not the day of the contest, where he was slightly smoother AND used too much oil. The all-time best Sergio condition was seen in the following shots taken in the days around but not during competition, in which he dried out. Still should have beaten Arnold that year though but it was still close enough that the decision was not a travesty. After '72 Arnold always made sure to be in top condition AND have a good tan.
In this shape, it's a coin-toss between Oliva & Arnold in their best-ever conditions. Who is better is just personal preference. IMO Arnold's '73 condition see here, and his condition in '74 were motivated by the possibility of Oliva's presence in the shows. Especially after the Mr. International situation in which Arnold sitting in the audience with Weider and Columbu declined Oliva's challenge to join him on stage in a more neutral setting than the Olympia allowed. Oliva never entered again against Arnold knowing he wouldn't be allowed to win.