Thats a tuff one, because in quiet a few pictures Arnold looks to have the wood on Sergio, thing is with Sergio Ive noticed in alot of his pictures just standing there he doesn,t blow you away as Arnold does, when Sergio opens up and starts posing he seems to transform alot in size, from most the shots @ the 70 World Arnold had noticeably improved his Quad mass from the 69 O and Sergio as has been mentioned alot b4, had way too much oil on blurring too a certain extent what Definition he had, i think the right result was Arnold winning the 1970 World because of the improvements Arnold had made and Sergio showing up Smoother than he had in past years couple that with the Oil issue, glaring lights etc.
Sergio did have alot of oil and in some shots appears very soft (particularly the relaxed pose, which is one of the worst poses for him), but in other shots he shows quad separation and hardness on par with Arnold's, and good detail through his upperbody. The comparison you posted with Arnold vs. Sergio shows them in proper lighting. You can see the detail between quad and ham, the true thickness of Sergio's chest, arms and the definition in the arms. Not to mention, Arnold's massive chest, arms and legs. Arnold generally does appear more impressive and from a combination of all the shots, but that is partly because there are more good quality shots of Arnold than there are of Sergio. I honestly couldn't decide without more pics of Sergio.
Draper holds his own but I think he is too small in musclesize and less aesthetically appealing then the top 2.