Nagato actually is but for this thread I would say Obito because he has only been hit by a single person and that person was minato the other time he was hit is when naruto and kakashi acted in tandem with one another and I dnt really count edo's because they aren't alive but even if I did edo Madara still wouldn't be the most powerful because he won't be able to truly defeat another edo, because he has no sealing techs someone like edo Nagato or itachi, or hiruzen who are edo's with sealing techs can beat edo Madara because edo vs edo would just go on forever while edo Madara vs edo Nagato would eventually end with edo Madara having his soul ripped out or sealed by totsuka from itachi, or death reaper god from minato and hiruzen but if we are going off the most powerful people when they were alive I would go with either Nagato or Minato simply because minato has never been hit and the largest part of fighting is getting hit which is the greatest feat u could have being a shinobi and well Nagato is God like and too many people have said such even more so than other shinobi have said for hiruzen and hashirama, and shinobi like Obito who knws everything about Madara and hashirama said Nagato was invincible and zetsu who is the closest person to Madara after his defection of the village said Nagato was unbeatable even in his weakened state the 2 people who knw more about hashirama and Madara than anyone said this so...