I wouldn't say Stiverne is untested. Arreola is decent gatekeeper level and he pretty much beat the **** out of him twice. The first one actually gets pretty difficult to watch after a while.
Stiverne has to be the favourite in this fight. He has a chin, he can bang, and has skills. Wilder has no chin, he does have power but looks sloppy with it. Doubt its going to be enough against a skilled opponent who's going to be hitting him back.
Majidov is prolly the standout heavyweight from the amateurs.. I know he lost a few times in the WSB but he's got the complete package for a HW. AKA right hand.. hook.. and a jab/right hand combi. Russo to me lacks power at the heavier weights. Maybe over 12 he woulda KOd him.