Gekishin takes it imo.
- As far as the two commanders in chief are concerned, Gekishin is superior. Reiou, one of the Fire Dragons, did receive hype by Gohoumei as a "cold and ruthless strategy who was feared even by my father" and he and his army had Tou deciding to retreat. However, I don't remember many other notable moments and particularly notewhorty feats, despite this being his first and last arc.
Gekishin was considered a hero for Yan, a legend in China with experience and someone who had the talent to riproduce Gakuki's warfare. He was able to see through the strategy employed by Riboku.
- Their armies : Reiou has Ranbihaku, who is clealry a strong warrior, Ouki and Kyou found him troublesome. While Gekishin does not have such a subordinate under him, he has a 10k Quanrong army. We've seen in the manga that the Quanrong are beasts, as far as fighting goes. Above the plain soldiers. When it comes to the poison cats Gekishin has are renowed for the tracking capabilities - finding the enemy HQ for example - and are called "soundless assassination army". Frankly, in a complex terrain like Sanyou, their capabilities could prove to be lethal.
I think there's a chance that Reiou could receive visits at his HQ and that Gekishin would end this war very soon. Even without that, I see Gekishin making the superior manouvers and getting the W. Ranbihaku being used as a piece by Reiou is certainly another threat but he can be taken care of and, if necessary, slain.