Board Thread:Naruto Discussions/@comment-27202380-20151124031155/@comment-5936871-20151124031521

Third Raikage was stated to be the greatest Raikage that Kumogakure ever had, so he was likely the strongest. As for all the other First Kage, all we can assume is that they were all pretty strong since they lived in Hashirama and Madara's era.