From the days of the old, the world of Naruto has seen the existence of individual clans. In the Warring States Era, Masashi Kishimoto, Naruto's author, showed the fans quite a diversity of clans who were at each others' throats in the quest for supremacy and at the top of the two ladder were two main clans – the Uchiha and the Senju.
Their rivalry was such that every other clan simply hired the other when they had to deal with a threat from one of them. Even decades later, when the shinobi villages had already been established, the Uchiha and the Senju remained to be two of the most powerful clans and produced some incredible shinobi. While the Senju certainly were incredibly skilled, the Uchiha proved on countless occasions that they were, in fact, the strongest clan in the story.
The Uchiha And The Senju Clan
Both the Uchiha and the Senju are quite special in the Naruto world and much of that has to do with their origins. Unlike most clans, these two are directly linked to the strongest characters in the entire story – the Otsutsuki. Following the arrival of Kaguya Otsutsuki on earth, she gave birth to Hagoromo and Hamura Otsutsuki, both of which were incredibly powerful. When their mother was corrupted with power, they sealed her away and Hamura kept a watch on her on the moon. Hagoromo, on other hand, had two children, Indra and Asura Otsutsuki.
Indra was immensely talented with jutsu and excelled at everything he did, being labeled a genius because of it. Asura, on the other hand, had great vitality, however, that was about it. His skills were nowhere near those of his brother and he needed to put quite a lot of effort in to get even the simplest of tasks done. Yet, Hagoromo eventually chose Asura as his successor, which led to a feud between the two brothers. Following Hagoromo's death, Indra swore vengeance on his brother and thus the cycle of hatred began. Indra's descendants came to be known as the Uchiha, while Asura's descendants became the Senju Clan. For centuries, these two clans dominated the world of ninja as the strongest to ever exist and were, more often than not, neck and n eck with each other.
Why The Uchiha Are The Strongest
While both the Senju and the Uchiha are extremely powerful, the Uchiha have produced countless mighty shinobi, compared to just a handful of the Senju. Apart from Hashirama, Tobirama, and Tsunade, no Senju Clan members made a legendary name for themselves. As for the Uchiha, the story has seen the rise of quite a lot of them to legendary heights showing that, as a clan, the Uchiha simply appeared to be superior. Being the descendants of a genius, it's no surprise that the Uchiha were incredibly powerful and grew strong at younger ages. Every member of the Uchiha clan was blessed with the power of the Sharingan, which carried a piece of the power of the Sage of Six Paths.
While the Senju did have great vitality, and a good mastery over all the ninja skills, they lacked that extra bit of touch that the Uchiha carried. Although some, like Hashirama Senju, were mighty powerful and even a match to Madara Uchiha, the vast majority of the Senju weren't all that impressive.
Furthermore, the Uchiha also carried the great power of the Forbidden Jutsu of the Izanami and the Izanagi. With these abilities, every single member of the Uchiha clan gained the power to either control reality and manipulate it however they want using Izanagi, or to decide the destiny of those around him using Izanami. Furthermore, being affected by Indra's vengeance, the Uchiha clan members were all bound by the Curse of Hatred. The stronger their hatred, the more powerful their Sharingan. Having grown on the battlefield, most Uchiha had quite powerful eyes and this made them even more dangerous as their hatred grew. Additionally, with a fallen comrade, the Uchiha could gain access to the Mangekyo Sharingan as well. Although it is strange that only a handful of Uchiha clan members awakened this power despite being in constant wars, those who did got immensely powerful.
At the same time, the Senju clan ceased to exist at some point in the Naruto series. After Hashirama and Tobirama Senju's deaths, the only living Senju seen in the story was Tsunade. The clan doesn't seem to exist anymore while the Uchiha are still a part of Konohagakure despite the Uchiha Clan Massacre that was carried out by one of their own in Itachi Uchiha. While every clan in Naruto is special in its own way and carries great significance to the plot, the Uchiha, as a clan, played the biggest role and it is no surprise to see them be the most powerful and important clan in Naruto.