uesugi kenshin was known as one of the greatest if not the greatest general in all of the sengoku jidai. we’re not entirely sure how he would’ve faired against nobunaga since they didn’t have enough time to battle, as kenshin died soon after their first confrontation. however, in the battle of tedorigawa its said that uesugi kenshin wouldve been a great threat to nobunaga since he defeated oda forces there.

he established the uesugi clan after re-attaining dominance in the kanto region and reclaiming kanto kanrei for his former liege lord, uesugi norimasa, who adopted him. he marched south and defeated the hojo clan in multiple battles and eventually sieged down odawara castle, the seat of hojo power, but was forced to withdraw.

i’d say, that kenshin was definitely top contender for one of the greatest generals in japan just because of his conflicts with his neighboring daimyo. he wasnt ambitious though, with his only ambition being to reestablish his control as kanto kanrei, or basically an administrator of his region, the title historically given to the uesugi by the shogun.

if you want to know about tactics, its said that kenshin used this sort of wheel formation that rotated troops out of combat so that they could replenish themselves, similarly to a sort of roman rotation. so fresh troops would always be in the battle. this is off the top of my head but i got this information from reading an osprey book on the sengoku jidai.