That is a hell of a question who could take down madara by solo. I think solo is impossible, to take madara you need eyes, strenght and speed. I would say Sasuke for the eyes and strenght and naruto for the speed and strenght. But that would be a duet, if 1v1 the only person comes in my mind is nagato. He has eyes and paths. He could put a hell of a fight, but I'm not sure if he may really take down Madara