In the "Naruto" series, several characters wield unique and powerful swords. Determining the "best" sword is subjective and can vary depending on individual preferences. However, here are a few notable swords in the series:

1. Samehada: Samehada is a sentient sword that belongs to Kisame Hoshigaki, a member of the Akatsuki organization. Samehada is covered in scales and can absorb the chakra of opponents, making it a formidable weapon.
2. Kusanagi: Kusanagi is a legendary sword associated with Japanese mythology. Orochimaru, one of the main antagonists in the series, possesses a sword named after Kusanagi. It is a long, straight sword with various abilities and is symbolic of Orochimaru's power.
3. Nuibari: Nuibari, also known as the "Sewing Needle," is one of the swords wielded by the Akatsuki member Kakuzu. It has a long, thin blade with a pointed tip and is adept at piercing and sewing targets together.
4. Kubikiribocho: Kubikiribocho, also known as the "Decapitating Carving Knife," is a massive sword wielded by the Mist Ninja Zabuza Momochi. It has a broad, curved blade and is known for its cutting power and durability.
5. Hiramekarei: Hiramekarei is a unique double-handled sword wielded by Chojuro, a member of the Seven Ninja Swordsmen of the Mist. It has the ability to change its shape and form to various weapons, including a blunt club or a longsword.

Each of these swords possesses distinct abilities and characteristics that make them formidable weapons in the "Naruto" series. However, the effectiveness of a sword often depends on the skills and techniques of the wielder.