I'm actually rooting for Jack just because things will be mightily shaken up if Heracles loses.
It's not just a case of "if Heracles wins, he loses". The converse is true: "If Jack wins, humanity loses", because Heracles was their sole champion in the pantheon.
Never thought a braindead meatheads' fighting manga would actually be anything more than a guilty pleasure, but there are some levels of irony in the current fight that make this series a delight.
Another hint that Heracles will lose is that Brünhilde said the gods would try their hardest to win the fourth round. So the author was playing Heracles up from the beginning, which is nine times out of ten a defeat flag.
I also hope there's no flashback to Jack. True evil should remain incomprehensible. He should just win while spouting Victorian values nonsense.