I dislike including Edo's, they show us the power of different ninja. Not only that, but they generally have regeneration and unlimited chakra. I like to judge the strength of the user by their arsenal and what they can do.
Without his arms, I'd say he is top 25. With them he could be top 20.
Though, with his Zetsu body and the possibility of him having Sage Mode, he moves up to either top 15 or 20 (Assured).
He's an animal and a beast, but we've never truely seen anything but summons and low grade ninjutsu from the man!
In his fight with Hiruzen, he sat back and let the Edo Kage deal with him.
Against Naruto, his greatest feat, he was injured and armless yet he held and toyed with the best.
Orochimaru on his deathbed could have defeated Early Part Two Sasuke, but he went to take his body and was over powered there.
He even ****ed with Itachi's Susano'o, and scoffed at being impaled until he realized the sword would seal him.
Also, he is by far the most intelligent and knowledgeable shinobi in the series. If we see him using some more jutsu, useful ones that aren't his various (weak, I hate to say) snake techniques, then Orochimaru with arms is top 20(Without a doubt). And MAYBE, MAYBE DSM would be top fifteen, closer to top ten.
