So here is my list it is a little different than yours.
1. Madara- obviously even the 4th Hokage knew he was too powerful. And anyone that can completely control the 9-tailed demon fox i mean come on naruto can't even do that yet.(Sasuke can somewhat but he couldn't completely control it like Madara yet)
2. Minato- Yeah I know he's dead but he fought and sealed the 9-tails into his own son and was a genius.
2. Naruto- yeah i put him as tied with his dad for now. Even Minato couldn't use Sage mode the way Naruto could. And eventually Naruto will learn Flying Thunder God jutsu. He completed his dad's jutsu as well the Rasen-Shuriken which we have all seen totally owned pain.
3. Nagato- Rinnegan enough said. Well actually he could have been the strongest i think if he had not went through all the crap he did because of Hanzo and Danzou. And if he had more time to train.
4. Jiraiya- he fought pain alone and took out some of his bodies even though they came back. Pain pretty much destroyed the whole village before Naruto got there. He destroyed more of pain's bodies than anyone by himself besides Naruto.
5. Itachi- yeah may have been able to beat J-man but we are not certain i mean he did run away. Look at what he did to Kakashi. He could have fought him without killing him but he didn't becasue he wasn't sure about fighting J-man. Sasuke could not have beaten him if he were not already sick and dying. And he planned for Sasuke to take his eyes anyway to fight Madara. Even though Madara is using Sasuke right now. this overall list