Oliva's almost total lack of upper arm detail is always disappointing; it takes away from the fact that his arms, overall musculature and tapers were on a relative basis better than Arnold's. If his arms and physique overall had muscle maturity and more refinement, i think it would be easier to say he had an edge. His shortcomings there countered his clear advantages in other aspects mentioned above. It's only in the occasional pic in his very best shape that you see any hint of detail. Arnold went much further and acquired great muscle maturity and refinement in '73, Sergio did not. Oliva says now that in hindsight it would have been better for him to have continued training with Arthur Jones; having someone push him made a big difference, clearly.
A great BB should do everything possible to address deficiencies, as Arnold did to bring up his calves and get real lean in '73 especially. I don't think Sergio went that extra mile with arms especially and his physique in general, in large part because it seemed that he didn't have the diet discipline and attention to detail required re: exercises to bring out more muscle maturity and refinement.
You could say the same about Arnold's thigh size, but i think it was genetic because they were in fact fairly large when he was at higher bodyweights, and seemed to be the first thing to shrink when he got leaner. Given that limitation, he did the right thing by focusing on getting them really cut and by drawing attention away from their shortcomings with great calves and posing.
I always give Arnold a slight edge now, based on having gone that extra mile to address the small things that make a difference when it's close, in '73 and '74.