Would not have Moubu and Kanmei in A+ unless this is purely based on strength. On overall ability, there's no way they rank with Ouki and Renpa, neither does Houken for that matter. Based on overall, Ouki, Renpa and Riboku (presuming he has at least reasonable strength) are worthy of A+ from those we've seen in the manga. Tou and the Duke are the next closest. By virtue of hype, the other 6 great generals of Qin, the 3 Zhao generals and those of similar status are A+ candidates too.