hirzuzen and minto where tied for the strongest hokages that was stated but j man wasnt a hokage so he could of been stronger but idk sm does make him hella stronger so he would put up a good fight
In his old age, then Jiraiya definitely.
But back in the day, Sarutobi was... well the word "strong" would be an understatement. He was hailed as the "god of shinobi", he had MONSTROUS chakra levels, he mastered every technique konoha had to offer. more than oro and kakashi combined probably. He was also considered the most powerful kage of his time, and we all saw how frickin overpowered the third raikage was.
in hiruzen's prime, Jiraiya gets curb stomped.