Naruto's hardest fight was during his encounter with Kaguya Otsutsuki. He may have won against Kaguya, but without Sasuke, Sakura, and Kakashi's help, he wouldn't have defeated Kaguya.
Pain. Arguably the greatest fight in Naruto, Naruto Uzumaki versus Pain marks one of the highest points of the entire story. The fight takes place in the Pain's Invasion arc where he attacks Konoha in search of the Nine Tails.
1 Baryon Mode
This jutsu used their chakra as raw materials to give rise to incredibly potent energy, akin to nuclear fusion, that far exceeded anything seen in the story. Using this energy, Naruto was able to access a form known as Baryon Mode.
Naruto beat Pain in the series, and this was canon. However, despite entering Sage Mode, Pain was able to drive him to a corner. Towards the end of the series, Naruto did receive powers from Hagoromo, which put him on a whole new level.
An immensely powerful goofball, Hashirama Senju is arguably the strongest ninja in the entire Naruto universe, with the exception of Naruto and Sasuke.
Kaguya Otsutsuki is easily the most powerful opponent that anyone in Naruto has had to face, and she is the final boss of the series, so to speak. Naruto has absolutely no chance of beating her on his own.
1) Kaguya Otsutsuki
As an Otsutsuki member, Kaguya is the strongest character in the Narutoverse. However, after consuming the entire Chakra fruit for herself from the God tree, she attained godly feats, making her an unstoppable force in Naruto.
Kaguya Otsutsuki was easily the most feared character in Naruto Shippuden. She was able to instill fear in every character that laid eyes upon her. Her main goal was to cast the Infinite Tsukuyomi upon the entire world so she could create another chakra fruit and reclaim all of her chakra.
Hokage (火影?, literally "Fire Shadow") Kage of Konohagakure. Currently Naruto Uzumaki is the Seventh Hokage.
1) Hashirama Senju
He was unmatched in power during his lifetime and even after death. Hashirama was undefeated in his lifetime.
Furthermore, Naruto had a hand in the defeat of Urashiki Otsutsuki.
Naruto and Sasuke are arguably the most powerful characters by the end of the Naruto Shippuden anime, so it goes without saying that Might Guy would stand no chance against Naruto in his Sage of Six Paths mode, or against Sasuke using his Rinnegan.
While there's no denying that Itachi is powerful, Madara is simply stronger, whichever way you look at it. With the powers of the 10 Tails and the Six Paths at his disposal, Madara is miles ahead of Itachi, and there's no way the latter can even put up a fight.
Over the years, Naruto Uzumaki has grown several times stronger, and the power he has now ensures that he surpasses Madara Uchiha in terms of strength. There's no doubt that Madara is an exceptionally powerful character, but Naruto outdoes him in nearly every way.
3 Naruto Defeated Sasuke With Half His Power
Despite that, he was able to keep up with Sasuke and even defeat him eventually, as evident from when Sasuke admitted to having lost to him in the end.
Naruto: 10 Powers That Make Kaguya Otsutsuki An Absolute God - IMDb. In the renowned series Naruto created by Masashi Kishimoto, Kaguya Otsutsuki is a character who can be considered to be the main catalyst triggering the various events and conflicts that take place in both the manga and anime.
During Naruto's training, he meets the Nine-Tailed Fox. Naruto's mind travels to his own body and sees the giant beast for the first time. Naruto is afraid of the scary creature, who emits evil energy. The entire encounter felt surreal, and Naruto was terrified that such a monster was really inside his body.