Being Australian, Kostya was my favourite fighter but I am gonna go with GGG here. Golovkin has got a way better chin. Kostya was a more explosive 1-2 combination puncher, better hand speed. Middleweight champ, historically, a lot more cred than 140 pounds. Also Kostya lost in his younger years to a lesser type fighter in Phillips and by stoppage. It took two rip offs at 35-36 to end G's undefeated reign. As much as I loved Kostya, I think Golovkin clearly. Also Kostya had more of an opportunity than Golovkin, Golovkin was older when he hit the states and had not been allowed to flourish as he should have. Kostya had a free run at the pro ranks from the beginning.