Why Jiraiya(especially SM) > Susano'o
The Jiraiya vs Itachi threads never cease. Here's another Jiraiya vs Itachi thread. Or rather a Swamp of the Underworld vs Susano'o thread.
If Jiraiya does Swamp of the Underworld under Itachi position, how does he escape. Jumping out of the swamp is impossible seeing as how the swamp's diameter/circumference is too large to just "jump" out. Susano'o/Uchiha's can't fly. Amaterasu won't help. Tsukuyomi/genjutsu won't help unless Jiraiya stupidly gets close to Itachi and looks him in the eye. Fireballs won't help. Nothing. AND HERE'S WHY(PROOF).
Here we see Jiraiya's Swamp of the Underworld while he was drugged by Tsunade. He also said that he was at about maybe 30% in combat performance, and yet he still managed to pull this off...
Here's a scaling of Itachi's Susano'o. Note: Itachi is 5'8"
If you use a ruler, or some type of item of measurement, you can clearly see that Itachi's Susano'o is approxemately 5x taller than he is. That would mean it's, give or take, 29 feet tall. So basically, if Orochimaru's snakes were capable of being subdued by 30% base Jiraiya's swamp, then Susano'o would be completely submerged.
And after all of this, we haven't even seen how big a Sage Art: Swamp of the Underworld would be. Hell, probably the size of a lake considering how much senjutsu does for ninjutsu.