The Susanoo is one of the strongest powers that are available to those of the Uchiha that have awakened the Mangekyo Sharingan in both eyes. Described as the strongest defense in Naruto, the Susanoo manifests as a giant humanoid made from the users' chakra, and it is capable of acting on their behalf. It was first introduced to us by Itachi Uchiha as his ultimate trump card against Sasuke, and with time, many others displayed the power to use the Susanoo as well.
Although it can be awakened by every Uchiha with two Mangekyo Sharingan, its powers differ from user to user. Here are all seven Susanoo users in Naruto ranked according to their strength.
7 Shisui Uchiha
One of the famed Uchiha prodigies, Shisui was a Konoha jonin with exceptional talent and skills. At some point during the Third Great Ninja War, Shisui witnessed someone close to him die, which led to him getting the Mangekyo Sharingan. Since he possessed it in both eyes, he also had the ability to wield the Susanoo.
In Naruto Shippuden: Ultimate Ninja Storm Revolution, Shisui's backstory revealed that he was, in fact, capable of using the Susanoo. While his version of this ability wasn't complete, probably because of having one eye stolen by Danzo, it was still powerful enough to take on a battalion of shinobi.
6 Itachi Uchiha
Also known as the Clan Killer, Itachi Uchiha was the elder son of Fugaku Uchiha, who quelled the Uchiha uprising in a single night by massacring his entire clan. Renowned for his Mangekyo Sharingan, Itachi awakened this ability when Shisui Uchiha committed suicide right in front of him. Consequently, Itachi got access to these powerful eyes, also granting him the ability to use the black flames of the Amaterasu, and cast the all-powerful Tsukuyomi genjutsu.
The third power of his eyes was the Susanoo. First introduced in his fight against Sasuke, Itachi's Susanoo was special. Although it wasn't a Full-Body Susanoo, it possessed two ethereal weapons which made it invincible. How strong it would've been in comparison to a Full-Body Susanoo is unknown, but it would likely be a tad weaker.
5 Madara Uchiha
One of the strongest Uchiha of all time, Madara was the first person seen in the series to have manifested a Full-Body Susanoo. As a kid, Madara awakened his Sharingan earlier than usual, and his progress didn't stop there. Soon, he killed his best friend to get his hands on the Mangekyo Sharingan, and after his brother's death, he transplanted his eyes to make his own Mangekyo Sharingan eternal. With the powers of the EMS, Madara Uchiha could combat against Hashirama on par for at least 3 days.
It also allowed him to manifest a Full-Body Susanoo, which dwarfed even the mountains. Wielding this godly strength, Madara could match the strongest shinobi of that era, Hashirama Senju. Although he ended up losing most of the time, Madara's usage of this ability was exceptional, and he even used it on a Tailed Beast.
4 Indra Otsutsuki
The elder son of Hagoromo Otsutsuki, Indra was considered to be a fighting genius ever since he was a little kid. His fighting prowess was such that nobody could stand up to him in combat. As a result of inheriting his father's strong chakra, Indra had the Kekkei Genkai of the Sharingan which, over time, evolved into the Mangekyo Sharingan. As a virtue of the powers offered by this legendary Kekkei Genkai, Indra was capable of using the Susanoo.
Unsurprisingly, Indra could manifest a Full-Body Susanoo even though he didn't have an Eternal Mangekyo Sharingan. In terms of powers, his Susanoo was mighty enough to match Ashura Otsutsuki in battle, and even corner it to some extent. Without a doubt, Indra was an exceptional Susanoo user.
3 Kakashi Hatake
Although a non-Uchiha, Kakashi possessed the Sharingan right from the beginning of the series. Years ago, during the Third Great Ninja War, Obito gifted one of his eyes to him while dying, and in the process, gave rise to the legend of 'Kakashi of the Sharingan'. In early Naruto Shippuden, Kakashi is seen using the Mangekyo Sharingan as well, and his control over this ability only thrived over time. Right towards the end of the Fourth Great Ninja War, Kakashi was endowed with both of the Mangekyo Sharingan by Obito, along with his remaining Six Paths chakra.
Combining the two powers, Kakashi awoke the Full-Body Susanoo which could even combat Kaguya Otsutsuki. Although the power-up was temporary, it amplified Kakashi's abilities beyond that of any shinobi for that specific time, and made him completely invincible in the process.
2 Sasuke Uchiha
The strongest Uchiha of all-time, Sasuke rose from being a regular Uchiha to a person who now wields half the powers of Hagoromo Otsutsuki. During the Fourth Great Ninja War, Sasuke got access to the Eternal Mangekyo Sharingan after transplanting Itachi's eyes. By the virtue of the Eternal Mangekyo Sharingan, Sasuke awoke to the Full-Body Susanoo as well, which was empowered by Six Paths chakra, just like Indra's.
To take his powers a step beyond, Sasuke drained the chakra of the Tailed Beasts and used it to empower his Susanoo even further, becoming the first and the only person to awaken the 'Indra Susanoo'. Its strength was enough to completely outclass Naruto's Kyuubi mode, even though the latter had more physical power and higher reserves of chakra.
1 Hagoromo Otsutsuki
The strongest character in the entire series, Hagoromo Otsutsuki was also a Susanoo user, at least in the anime. Due to the evolution of his Sharingan into the Mangekyo Sharingan, Hagoromo gained access to the powers of the Susanoo. Thanks to his Six Paths chakra, he could manifest the Full-Body Susanoo right away, and his version of this ability was remarkably large, matching even the Ten-tails in size.
Its capabilities were great enough to outclass Kaguya Otsutsuki, who had fused with the God Tree to become the Ten-tails itself. Hagoromo went on to awaken the Rinnegen shortly afterward and gained further power, essentially rising to the status of a God in the process.