I am going to omit the SoSP, because it is all a bunch of hearsay with him and his descendants. So!
Minato- We saw him fight Madara/Tobi and the 9-tails while protecting a baby and the village.
Itachi- I really think Minato and Itachi are in a league of their own. Itachi, like Minato, was fighting with other demands in mind. He had to kill Orochimaru, for example. Susanoo and his intelligence put him way ahead of the game, and I do not think Itachi's story has been fully told.
Naruto, full-power. Strong enough to mutilate Kisame with one hit. Near-infinite chakra at this point.
Sasuke. He has a ton of tools and he is a very smart fighter (Deidara fight).
Tobi/Madara- Weaker than he might have been even when fighting Minato, but still able to survive some brutal attacks.
Pain- Really strong, but we saw some of his weaknesses: needs to be close to his bodies, and sage mode Naruto was fast/strong enough to crush some of the bodies, Rinnengan or not. As strong as his attacks are, Minato and Naruto can hit him before he reacts and the Sharingan/Susanoo could eliminate his defenses.
Third Hokage- Knew tons of Jutsu, was strong into old age.
Kabutomaru/Sage-mode Jaraiya- Speculation here, but both Orochimaru and Jaraiya barely survived the 4(? maybe more) tails cloak. I imagine Sage-mode Jaraiya and Kabutomaru to both be stronger than that.
Kisame- Guy was a monster, but he was also really smart. He showed adaptive strategies when he fought Bee.
This is purely based on what I have seen, so the first Hokage does not get a spot. I am speculating about Kabutomaru, yes, but I would still put Orochimaru right around that position, so it does not really change the list.
Honorable Mentions:
Tsunade
Bee
Kakashi
Danzo
Raikage
Hanzo