GGG all the way. Hagler lost that because he was not a fully developed fighter. Golovkin has no such problems with his massive am career.
I see the "Worm" in an upset. Monroe was one of those fighters if a fighter came in underestimating him,he could slip and slide his was to a victory. Say over a 3 fight series,on that 1st fight bases Monroe could upset Triple G. Triple G,would adjust in fight #2and#3 Triple G. Would knock him out.
Against the GGG that labored to a close decision over Jacobs?.... I would take The Worm by decision. But, it appears that GGG may be slipping quite a bit at this point. On his best night, GGG probably lands enough hard leather to squeak out a UD.