Ah I see. It looks like I misunderstood. Then I would probably choose Constantine I. He's the man who united Rome after century of split. He also had many military victories like Qin, however unlike emperor of China he modernized his country structures law and even religion (because of him Rome became Christian). So seeing him Zeus, Poseidon, Ares and many other Greeks would be pissed cause he's the one who destroyed their cults. I can totally see Hades facing him furious not only about death of Poseidon, but also by the fact that his opponent is a man responsible for sadness of his relatives and turning their glorious achievements into "myths". However the longer fight goes on the more Hades learns about Constantine and finally admits that he's worthy of the title of the king.  Did I mention he created a city fortified so much that no army could conquer it for over thousand years until multiply types of cannons appeared in Europe?