Jiraiya. Especially if he starts in SM.
Only chance Itachi has is to outsmart him and get him in Tsukuyomi. Any other method of combat is dealt with.
Taijutsu: Itachi isn't blitzing someone in SM, lol. Nor will he defeat frog kata.
Genjutsu: Itachi's only chance. Normal genjutsu won't work since Jiraiya has ma and pa to snap him out IF he gets caught. And Jiraiya is already skilled at breaking genjutsu.
Ninjutsu: In terms of arsenal, Jiraiya landslides this. Amaterasu gets sensed or shadow cloned out of. Susano gets lawl-swamped. Totsuka blade gets sage dodged.
Itachi is very smart. He's very good. Almost perfect. But his abilities are still limited as is his chakra levels.
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As for people saying Jiraiya doesn't have sensing or frog kata, it was NEVER stated that he didn't have those. He just never showed them exclusively like Naruto did. Jiraiya trained under Fukasaku at Mt. Myoboku just like Naruto and Minato. He underwent the same training. Jiraiya being an imperfect sage just implies he can't enter/maintain SM on his own.
Why didn't he sense/dodge the Asura path attacking him from behind and blowing off his arm? That's forever unexplained. Even IF Jiraiya couldn't sense, he still had Fukasaku and Shima, 2 PERFECT sages on his shoulders. Surely they should've sensed it. Kishi only gave out sensing and frog kata to Naruto later to give SM more flexibility.
