Itachi without a doubt. Kisame himself admitted to being weaker than him to Itachi himself. They were discussing Jiraya and Kisame said he knew he couldn't beat Jiraya. To which he said he thinks Itachi could. This all I need to say. Itachi wins. No shadow of a doubt in my mind.
@highaccuser Okay didn't see the Kage Summit bit on Sasuke my bad(doesn't change much though still the same result). I recommend you edit Opening post to include the nerfs to each character like Danzo having no use of Shisui's eye(cause that is not explained at all in OP) and Reanimation is also not mentioned anywhere.
I'm gonna assume this is Sasuke EMS and not current Sasuke. And that Kakashi is War Arc Kakashi.
Naruto vs Jiraya = Naruto wins. He has greater use of Sage Mode and his Wind Style RasenShuriken is something you don't want to mess around with.
Deidera vs Kakashi = While a very close fight I have to say I think Kakashi wins.
Orochimaru vs Might Guy = While some will say Might Guy wins I personally believe Orochimaru wins. Why you ask? Orochimaru is a researcher and so will know how the technique works. He will then know that he just needs to not die until Might Guy has gotten out of 7th gate. Orochimaru then kills him.
Kakuzu and Sasori vs Danzo = Team wins. Without Shisui's eye Danzo would lose in my opinion but with it he wins. Danzo still will give one heck of a fight though.
Kisame vs Onoki = Gonna have to go with Kisame winning this one. Onoki may be very powerful but his back is just to much of a weakness. Plus Kisame has various ways he could win. Probably extremely close, but gotta go with Kisame.
Gaara vs Deva Path = Deva wins. Don't see how Deva could lose. Scratch that Deva can't lose. To much of a power level difference between the 2.
Kabuto vs Tsunade and Third Mizukage = Since Lord 3rd Mizukage's abilities are unknown gonna venture a guess he means either Lord 4th Mizukage(3 tails Jinchuiki Yagura) or Lord 5th Mizukage(Mei). In the end though I don't think it matters as Kabuto wins no matter who Tsunade's partner is.
Sasuke vs Tobirama = Again going to assume this is EMS Sasuke and not current one. In that case Tobirama takes the win with all his versatile abilities, speed, ingenuity, and cunning. Plus he can bring back a dead person if necessary to help whoop Sasuke's a$$ if he can't himself(and to make it clear I think Tobirama can whoop his a$$ even without help).
Naruto vs Kakashi = Naruto wins. Shouldn't have to explain this that much. Naruto is in a different League than Kakashi. Its that simple.
Orochimaru vs Kakuzu and Sasori = Gonna have to say I think Orochimaru wins. While a close fight in my opinion, Orochimaru can always resort to reviving some powerhouse to help him win. To be honest at the outset he was one of the favorites to win.
Kisame vs Deva = Deva wins. Kisame needs to be able to hit Deva in order to win and because of Deva's abilities that is impossible compared to Deva whose attacks can always connect. Deva can't lose this one in my opinion.
Kabuto vs Tobirama = A fight I'd very much like to see. In the end as much as I want to say Tobirama wins(as I'm a major fanboy of his). I can't really do that. I say Kabuto wins. He has a greater mastery of Reanimation and has to many different abilities for Tobirama to overcome. And Tobirama's usual edge(Intelligence) isn't an edge as Kabuto is also extremely good in this regard as well.
Naruto vs Orochimaru = While an extremely close fight probably gonna go with Orochimaru wins. Orochimaru is cunning, intelligent, and has the reanimation technique pretty hard combo to beat.
Deva vs Kabuto = Kabuto is extremely powerful and with Tayuya's Genjutsu in my opinion, Kabuto wins. Kabuto also has Reanimation, Cunning and Intelligence. And also did I mention he is a Sage who can keep Sage mode going almost indefinitely due to Jugo's kekkei Genkai?
Orochimaru vs Kabuto = Kinda funny how these 2 are the finalists. Both have the same edges and are extremely powerful. In the end though I believe the grand champion to be Kabuto. The simple reason is Kabuto's body can use Sage Mode while Orochimaru's can't. Even if Orochimaru could, he can't use it for almost an indefinite amount of time but Kabuto can.
So the winner of the Naruto bracket is Kabuto Yakushi.