Leonard by unanimous decision, with Golovkin's face looking a bit worse for wear. No disgrace though. If Leonard's eye had held up and he had managed more middleweight bouts, he was potentially a 160lb legend - not many could have managed such a close scrap with Hagler (although I recognize that he would always have peaked at welter).
The Leonard that fought Hagler was having his first fight for years and I would say was already way past his best by then. Against old Hagler, Leonard tried to time it so that the bout would be at the best time to fight Hagler just like Canelo tried to delay fighting GGG until now because he thought GGG would be past his best now. GGG though is still better now than the Hagler that Ray fought and I think he would be still too much for the returning Leonard in his first fight back. Leonard best hope would be the judges being conned by his short burst of flashy combos at the end of rounds and getting a undeserved decision.
I would take GGG over SRL in a similar fashion that he beat Canelo. I thought Golovkin fought well on Saturday night against a mature Canelo who is very well rounded and quite a talent.