I will go with Shibashou, though no confident since outside of Shibashou, Qin have the next 4 more talented commanders.
But I think having unity in an army is vastly more important, when talking about large scale war, compared to three different armies with no superior commander.
I have no idea how to gauge Kansaro, and Gaku in terms of strategic prowess compared to Mouten and Ten. Does Shibashou himself have strategical prowess or is he a pure martial general? No idea.
Yea the more I think this out, M3 will take it.