The Navy is one of the Three Great Powers in the One Piece world. The organization was created by the World Government to enforce the law and maintain peace throughout the world. The Navy has thousands of people within its ranks, which allows them to overpower criminals with sheer numbers.
As a group, the Navy is nigh unbeatable, with only the strongest pirates in One Piece standing a chance of matching their might. The Navy has lots of strong fighters, and they are armed with extremely potent devil fruits. As a result, the strongest devil fruits in the Navy allow their users to carry out their duties without fail.
The list is not ranked.
1 Magu Magu no Mi
The Magu Magu no Mi belongs to Akainu, who is the current Fleet Admiral. It is a Logia-type devil fruit that grants its user the ability to create and manipulate magma. The Magu Magu no Mi is said to have the highest offensive power out of all the Logia types, making it a very dangerous devil fruit.
Akainu demonstrated the power of the Magu Magu no Mi, during the Marineford arc, in which he instilled fear into the hearts of both pirates and his fellow Navy soldiers. Akainu was able to overwhelm and kill Portgas D. Ace with his devil fruit, thus effectively winning the war for the Navy. He even burned the left side of Whitebeard's face completely, once again exhibiting the devil fruit's ridiculous power.
2 Mori Mori no Mi
Introduced in the Wano Country arc, the Mori Mori no Mi is another Logia-type devil fruit that allows its user to control plant life at will. Judging by Ryokugyu's fight in Wano, the devil fruit doesn't seem to be limited to a single type of plant, so it's plausible to assume that he can create all kinds of plants.
The plants created by the devil fruit are capable of absorbing liquid from both living and non-living things. This ability is lethal, as it dehydrates the opponent and could even lead to their death. The plants created by the Mori Mori no Mi also seem to have a certain level of resistance to normal fire, although they cannot withstand stronger fire-based attacks.
3 Hito Hito no Mi, Model: Daibutsu
The Hito Hito no Mi, Model: Daibutsu belongs to the former Fleet Admiral, Sengoku. It is a Mythical Zoan-type devil fruit, and it enables Sengoku to transform into a giant golden Buddha. In his transformed state, Sengoku can create shock waves from the palm of his hand.
These shock waves were able to cancel out the power of the Gura Gura no Mi, which is a huge testament to its power. Furthermore, the devil fruit provides Sengoku with improved physical strength and stamina. Since Sengoku has only used his devil fruit a handful of times, the full extent of its power remains unknown.
4 Pika Pika no Mi
The Pika Pika no Mi is a Logia-type devil fruit that was eaten by Admiral Kizaru. As a Logia-type devil fruit, it allows its user to faze through attacks unless they are coated in Haki or if they have an elemental advantage. The user also has complete control over light, which grants them incredible speed and power.
A single kick imbued with the power of the Pika Pika no Mi was strong enough to destroy a huge mangrove with ease. As a light human, the user can move at the speed of light, making it impossible to dodge their attacks without Kenbunshoku Haki.
5 Zushi Zushi no Mi
Fujitora is the only Admiral that has a Paramecia-type devil fruit, but it is not weak in any way. With the power of the Zushi Zushi no Mi, Fujitora can manipulate gravitational forces. Fujitora can either use the devil fruit to put serious pressure on his opponent and stop them from moving. Or, he can bring down a giant meteor from the sky. Fujitora proved his strength when he managed to fight Sabo at Dressrosa, albeit neither of them was using their full power.
Fujitora's devil fruit has other uses too. It can be used to make an object float in midair by negating gravity. He can then climb the affected object and use it to get to different places. The versatility of the Zushi Zushi no Mi makes it one of the best devil fruits in the Navy.
6 Moku Moku no Mi
The Moku Moku no Mi is a Logia-type devil fruit that is currently in the possession of Vice Admiral Smoker. The devil fruit allows him to create and control smoke at will. It can be utilized to hold down weaker opponents, although it is futile against the stronger ones.
The devil fruit can be used to "fly" from one place to another, which is quite useful. Due to the non-lethal nature of smoke, Smoker cannot afford to produce large quantities of it, as this makes him an easy target for his opponents.
7 Ryu Ryu no Mi, Model: Allosaurus
The Ryu Ryu no Mi, Model: Allosaurus, belongs to X-Drake, who is also a member of SWORD. It is an Ancient Zoan-type devil fruit that lets him transform into an Allosaurus, a vicious prehistoric carnivore.
Like all Zoan-type devil fruits, the Ryu Ryu no Mi, Model: Allosaurus, can be used in various ways. X-Drake can either turn completely into a dinosaur or use the hybrid form for better mobility. X-Drake was able to become a Tobi Roppo thanks to the power of the devil fruit. However, despite his titles, X-Drake has failed to impress fans because of his underwhelming fighting abilities.
8 Woshu Woshu no Mi
The Woshu Woshu no Mi is a Paramecia-type devil fruit. It was eaten by Tsuru before the start of the story. Unlike some of the other powerful devil fruits in the Navy, Tsuru's devil fruit is not flashy, but it does have frightening potential. She demonstrated the power of the devil fruit in the Marineford arc, in which she incapacitated several pirates.
The characters affected by its power resemble washed clothes that are put out in the sun to dry. Oda has also stated that if the devil fruit's power is used against evil people, their hearts will become a bit less wicked.