Like any good anime, the main character in "Naruto" emerges as the most powerful.
Naruto starts off as a goofy orphan disliked by everybody, unskilled in ninjutsu and even worse at schoolwork. By the end, Naruto is the most powerful shinobi on the planet. In his basic human form he can create countless shadow clones, summon giant toads, and wield the awesome Rasengan. Then there's his Toad Sage mode, where he summons nature chakra to make him more powerful than nearly any other shinobi. He befriends the Nine-Tails and is able to control a Nine-Tails mode with a Six Paths Sage power, in the process making Naruto an absolute beast
Naruto single-handedly takes down Nagato's 6 Pains, despite the fact the whole Leaf Village could not. His shadow clones are able to take down whole enemy battalions in the Great War, and his Toad Sage mode allows him to be the only shinobi to distinguish White Zetsus from allies. Finally, he saves his friend Sasuke so they can combine their powers to save all of humanity.
Naruto's greatest power, however, lies simply in who he is. Tsunade, Kakashi, and others mention how Naruto makes you want to root for him, makes you want to befriend him. His optimism, loyalty, and dedication inspire everybody he meets.
That's the core of "Naruto": The ability to inspire is more powerful than even the strongest jutsu. Nevertheless, it is helpful to have a few strong jutsu up your sleeve.
2.Sasuke Uchiha
Sasuke Uchiha is the yin to Naruto's yang. Naruto starts off uncouth and unskilled; Sasuke is the coolest and most talented in their class. Naruto can't throw a kunai in the right direction; Sasuke can hit the bullseye without trying. Their rivalry fuels both to greater heights.
The only Leaf Village Uchiha to survive Itachi's raid, Sasuke dedicates his life to getting strong enough to exact revenge. When Orochimaru promises to make him even stronger in exchange for Sasuke's body, Sasuke trains to the point that he can defeat a battlefield of shinobi without killing anybody. His real gift at this point is his Mangekyo Sharingan, and with it he kills the powerful Orochimaru.
After Sasuke "defeats" Itachi, Itachi gifts him Amaterasu. Sasuke develops his own arrow-shooting Susanoo, enabling him to take down Danzo's "instant replay" Izanagi. Finally, Sasuke is granted Six Paths chakra and a Rinnegan.
All of which allows him to bring team 7 out of the Infinite Tsukuyomi that has trapped all living beings. These powers help him save the world alongside the friend who never gave up on him, Naruto.
3.Madara Uchiha
Madara co-founded Konoha with his best friend Hashirama Senju, possibly the two greatest shinobi of all time. In flashback, we see him fight Hashirama and we see Madara die. But he'd planned for this. Madara comes back to life using the Izanagi some time later, with Hashirama's flesh in his mouth to add Senju powers to his Uchiha arsenal, a brilliant bit of foresight.
Madara knows how to live long beyond any other shinobi, growing his power and learning to harness Hashirama's wood style and Rinnegan. Then he saves Obito, turning him into the superpower he becomes. He gives Nagato the Rinnegan, foreseeing his part in Madara's plan: Peace through universal enslavement.
When reincarnated, Madara defeats the Five Kage with his Perfect Susanoo. Reincarnated with his prime of life strength, but the Senju skills he only mastered in old age, his power is such that one wonders if any non-celestial could've defeated him.
So Madara dies three times and is more powerful than everybody during the Great Shinobi War. He created and controlled the two most powerful Akatsuki members from death. He also briefly becomes the Ten-Tail Jinchuriki. He could have ranked even higher than number 2 — if a good portion of his power hadn't been part of a scheme set up by Kaguya herself.
4.Itachi Uchiha
When it comes to raw power and ability, an argument could be made that Itachi's stronger than Sasuke. His genjutsu is such that he's the only shinobi to escape Kabuto's reanimation jutsu (except Madara). He outmatches Sasuke during their battle, and Sasuke only wins because Itachi allows it. As could be expected, considering Itachi single-handedly wiped out the strongest clan in the Leaf.
Itachi has always been a few steps ahead of nearly everybody. His foresight and abilities enable him to inspire his brother from the lam, coming full circle when he uses his fight with Sasuke as a way to rid his younger brother of Orochimaru's curse. He likely foresaw that he would be reanimated by an Akatsuki member and get a chance to fully explain everything to Sasuke. This foresight probably inspired him to learn the time-loop jutsu Izanami, a necessity for fighting a powerful reanimator.
Sasuke's slight lead over his brother comes from the fact that not only did he do things his own way, he could change the direction of his and other people's fates. Itachi points out that possibly Sasuke could've convinced the Uchihas not to try and overthrow Konoha, thus preventing their slaughter.
If Sasuke and Itachi had a real battle, it's tough to say who would emerge the victor. Until Sasuke gets Six Paths chakra, the smart money is on Itachi.
5.Obito Uchiha
Few surprises in "Naruto" are as huge as the revelation that the man behind the mask running the Akatsuki is Obito Uchiha, Kakashi's fallen comrade, from whom Kakashi received his Sharingan eye. Admittedly, it's hard to have predicted that considering how Obito is depicted in the flashbacks as the weakest member of Minato Namikaze's team. Yet here he is, almost as powerful as Madara, even briefly taking the name of Madara because it turns out that he is, in fact, partly Madara.
A theme throughout "Naruto" is that our loyalty to those who care for and train us can make us blind to the evilness of our actions. No matter how much of Obito's power comes from himself, from Madara, or from Black Zetsu, he wields that power effectively.
Eventually Obito is a Jinchuriki host to the Ten-Tails, can wield the next-level Truth-seeking Balls, and even gives Kakashi his own Sharingan and chakra AFTER he dies. Since almost no great shinobi became powerful without gifts from more powerful beings, we can forgive how much he got from Madara. There's a reason friendships and alliances are central themes to "Naruto."
He's only down at 6th because if it weren't for Madara reviving him and giving him so much power, Obito would have died as a child.