Heres my theory on whos the strongest: Its really how the Hokages worked in my opinion, lets put it this way the first picked the second b/c he was stronger, then the second chose the third as the next hokage b/c he was stronger. The third learned every technique in Konoha but saw how much potential the forth had, so he chose him as the next Hokage knowing that he would indeed become stronger then him with time, so when you think about it each Hokage chose the next b/c they knew that, that Hokage would be stronger than him. So who do I think is the strongest? The Fourth of course.