First, these are the contenders who have yet to take the field:
Gods:
Buddha
Loki
Apollo
Susano'o No Mikoto
Bishamonten
Anubis
Odin
Beelzebub
Humans:
Qin Shi Huang
King Leonidas
Nikola Tesla
Grigori Rasputin
Okita Souji
Michel Nostradamus
Simo Hayha
Sakata Kintoki
Overall speaking, I can say that among the Gods the ones I want to see more of design are Beelzebub and Anubis, while on a fighting level I want to see them two more Loki. Among the Humans, on the other hand, the ones I want to see most are the most, namely Rasputin, Tesla, Nostradamus and Leonidas, while on a fighting level I want to see all of them plus Simo Hayha.
But ... I'm pretty sure none of them will take the field right now.
On the Human side, I think it is no coincidence that Qin Shi Huang has been revealed already now, even if it was the spin off of Lu Bu, and I think he will fight in the sixth match, instead for the Gods we will see in personal opinion one between Buddha and Bishamonten for what happened during the fifth meeting. I am almost certain that Zeus will punish them by having one of them take the field in the sixth match, but I don't think it will be Loki's turn (he seems an important character for the story) or even Buddha (the Volund question still needs to be investigated since for Loki that is only a theory), Bishamonten on the contrary is expendable, and considering that for me the sixth match will win the Humans will leave us even life (although he does not completely exclude Buddha in the sixth match, if it were his turn it would not surprise me at all).
Consequently my final answer is:
Sixth match: Qin Shi Huang vs Bishamonten
And I also add that for me Brunhilde will not be the last Valkyrie to make the Volund but the penultimate, the last will be Goll who will also prove to be the strongest Volund ever.