hypotheticals are fucking retarded, prime gunter is bigger and better conditioned than arnold, the rest comes down to your preferences in aesthetics.
No one of Arnolds era was conditioned like todays pro's, the science wasn't there. Today's 290 pound monsters don't work any harder than they did in the past, hell, in a lot of cases they work less. They just have access to substances that didn't exist 20-30 years ago, not to mention the nutrition of today.
While it's true that Gunter is bigger and better conditioned, it's also true that Arnold was the champion during the years he competed. This my friend is something Gunter can't say, but guys like Arnold, Haney, Dorian, Ronnie, etc can. Arnold has a timeless build that almost any of us wish we had. Fuck the weight difference, I still respect Arnold as a BB more than Gunter.