I think if Bas was in his prime in 2013, it would be a much different Bas... a much better Bas.
Don't forget, facilities were scarce- income was low, top medical coverage was nonexistent.
There was only so much at their disposal.
Wanderlei in his prime or not, probably wouldn't change how he is in performing in the UFC today.
He can't seems to hang with technical strikers. Even when he fought Stann, when he was going wild he was getting dropped. He only ended up winning because he started composing himself, and timing his shots... and eventually dropped Brian with a perfectly timed counter-hook.
I think Bas has a much higher glass ceiling compared to Wanderlei.
But again, it comes down to the setting as well. I think if the UFC allowed knees to grounded opponents and soccer kicks, Wanderlei would have done much better.
But also, Bas was knocking guys out with open palm strikes because closed fists weren't allowed.
Too many variables. We'd never really know.
Personally I'd say Bas based on a gut call.