I'm going to have to go with Hashirama....the man fought both Madara and Kurama (two of the most powerful and devastating combatants in the Narutoverse) at the same time. Also not that Madara was basically a prodigy with an eye technique that can track what the opponent will do. This means that Hashirama had to be able to use an attack that, while Madara could forsee what was about to happen, he couldn't stop it.
I would say that takes some considerable strength, endurance, and intelligence.........unless of course Kishi decides to change the fight entirely as a means to once again Hype up Madara