The Hito Hito no Mi, Model: Nika is one of the most powerful Devil Fruits to exist in the One Piece world. It is outright stated to be the most ridiculous power to ever exist and with its abilities, Luffy has grown incredibly overpowered, especially now that it has Awakened.
While this fruit isn't overpowered by itself, mastering and Awakening it means that the user becomes the Warrior of Liberation and is only limited by their imagination. As such, this fruit can become the greatest weapon up one's sleeve, if used properly. Very few people in One Piece possessed Devil Fruits that can rival the Hito Hito no Mi, Model: Nika, and even fewer can triumph over this power.
5 Magu Magu no Mi
The Magu Magu no Mi is a Logia type of Devil Fruit that was eaten by the current Fleet Admiral of the Navy, Sakazuki, also known as Akainu. This Devil Fruit allows him to produce as well as turn into magma at well. Being a Logia type of Devil Fruit, the user can easily avoid all damage that is thrown their way, unless it is Haki infused.
The offensive power of this Devil Fruit is known to be of the highest order in the One Piece world.
While cannot do the incredible things that the Hito Hito no Mi, Model: Nika can do, it is still very overpowered, as has been seen already over the many arcs of One Piece. This Devil Fruit, when Awakened, will become even more powerful and can certainly rival Luffy's fruit without too much trouble. Surely, the Magu Magu no Mi is one of the most destructive abilities to exist in the story so far.
4 Mero Mero no Mi
The Mero Mero no Mi is a powerful Paramecia type of Devil Fruit that currently belongs to the Snake Princess, Boa Hancock, who is also the leader of the Kuja Pirates. This fruit was force-fed to Hancock when she was a slave, after being kidnapped during her teenage years. Despite everything that she has faced, Hancock stands tall and strong as one of the most fearsome pirates in the world and much of that is down to her Devil Fruit ability.
While the Mero Mero no Mi doesn't function like the Hito Hito no Mi, Model: Nika, it is still overpowered and its own right. It allows Hancock to turn anyone who shows any kind of attractive feelings towards her into stone. In fact, even inanimate objects that are not attracted to her can be turned to stone within seconds. Its powers were such that even Blackbeard, an Emperor, knew that if given the chance, Hancock can defeat him by turning him into stone. While this ability doesn't work specifically on Luffy, on another user, it certainly can, making it an incredibly overpowered fruit.
3 Uo Uo no Mi, Model: Seiryuu
Eaten by none other than the former Emperor of the Sea, Kaido of the 100 Beasts, the Uo Uo no Mi, Model: Seiryuu is an exceptionally overpowered Zoan Devil Fruit. This fruit allows Kaido to turn himself into a giant blue Eastern Dragon capable of spewing fire, manipulating lightning, as well as producing wind blasts and slashes. Above all, it grants Kaido tremendous physical strength and incredible durability, which can only be bypassed with advanced Armament Haki and Conqueror's Haki Infusion.
This Devil Fruit made Kaido strong enough to overpower Luffy throughout the majority of their fight. In the end, Kaido ended up losing this fight, however, that doesn't mean that this Devil Fruit is not one to be held in a legendary light. It is certainly up there with Luffy's very own Devil Fruit and a power that could rival Joy Boy with ease.
2 Gura Gura no Mi
The strongest known Paramecia type of Devil Fruit to exist in One Piece, the Gura Gura no Mi the second ability of Yonko Blackbeard. Previously, it was used by Whitebeard, who was one of the Emperors of the Sea as well. This Devil Fruit allows its users to create incredibly powerful quakes out of thin air. They can even set off a tsunami if they want and use quakes in all their attacks, making them a vibration human.
Its powers are such that it is known to be able to destroy the entire world, as was exclaimed by Sengoku himself during the Paramount War. The Gura Gura no Mi can sink islands with ease and when pit against the Hito Hito no Mi, Model: Nika, this fruit certainly holds its own.
1 Yami Yami no Mi
Believed to be one of the strongest abilities to exist in One Piece and certainly the mightiest in the Logia class, the Yami Yami no Mi is the first known Devil Fruit eaten by Blackbeard. This fruit was found by Thatch, the Fourth Division Commander of the Whitebeard Pirates and was stolen by Blackbeard. Its abilities allow Blackbeard to control darkness at will. According to him, darkness has infinite gravity and can suck in anything, even things such as light.
The most dangerous ability of this Devil Fruit is that it can prevent other Devil Fruit users from exhibiting their powers by sucking in their abilities as well. Undoubtedly, this is one of the most dangerous powers to exist in One Piece and certainly an ability worthy of rivaling Luffy's Hito Hito no Mi, Model: Nika.