At this moment in time, it has to be Juuko. We are still somewhat guessing as to the true strength of Kansaro but even still, Man'U is the difference here. You are looking at a genuine, Q6 level monster. He beats whatever is in front of him and 3 of the 4 Seika commanders would happily duel him to their death.
The Juuko 4 army is basically similar to that of a straight up, GH/Q6 army with Man'U as its head and 3 very powerful generals underneath. You'd need Shibashou on this battlefield to give Seika a chance.