In the "One Piece" series, the Kitetsu swords are a set of cursed blades with a reputation for being extremely powerful. There are three known swords of the Kitetsu line: Kitetsu, Nidai Kitetsu, and Sandai Kitetsu.

Among the three Kitetsu swords, the strongest is the Kitetsu that is not numbered, often referred to as "Shodai Kitetsu" or "Yonkou Kitetsu." However, this sword has not been prominently featured or explored in the series, and its exact abilities or powers have not been fully revealed.

Nidai Kitetsu is the second in line and is currently in the possession of Trafalgar Law, a fellow pirate in the "One Piece" world. Nidai Kitetsu is a formidable sword, but its exact strength in comparison to the other Kitetsu swords remains unclear.

Sandai Kitetsu, the third and most well-known sword of the Kitetsu line, was obtained by Roronoa Zoro during the Loguetown arc. While Sandai Kitetsu is a cursed sword, it is also highly regarded for its quality and strength.

It's important to note that the true strength of each Kitetsu sword can vary depending on the individual's skill and ability to wield it. The reputation and power of a sword in the "One Piece" series often depend on the skills and feats of its wielder, as well as the narrative development of the story.