I know this is heresy but- Franco is underrated and Sergio is overrated. Not saying Franco is better than Sergio.
Sergio had ridiculous proportions, tiny waist, massive ribcage, massive arms, legs, chest etc but he was alway pretty smooth. Even by the standards of the day. Even in 1972, probably one of his best appearances, he looks great standing alone but Arnold is quite a bit sharper and Arnold wasn't even in the best condition. He was off quite a bit in 72 and still in better condition when they're standing next to each other.
Franco is crushing Zane in those pics. The 76 pics they are a bit closer than in 74 or 75 but Franco is easily winning thoses comparisons imo.