Determining the "highest quality" samurai sword can be subjective, as it depends on personal preferences, intended use, and various factors such as craftsmanship, materials, historical significance, and reputation of the swordsmith or manufacturer. However, there are certain factors to consider when looking for a high-quality samurai sword:

1. Traditional Craftsmanship: Swords made using traditional methods and techniques, such as those employing tamahagane steel and traditional forging processes, are often highly regarded for their historical authenticity and craftsmanship.
2. Authentic Materials: High-quality samurai swords often utilize premium materials, including carefully selected carbon steel for the blade, high-quality wood for the handle (tsuka), and genuine fittings (tsuba, fuchi, kashira) made from materials like brass, silver, or gold.
3. Blade Geometry and Balance: A well-balanced and properly proportioned blade is essential for optimal handling and performance. The curvature (sori), width, thickness, and profile of the blade are carefully considered during the crafting process.
4. Heat Treatment and Differential Hardening: The heat treatment techniques employed by skilled swordsmiths contribute to the hardness, flexibility, and sharpness of the blade. Differential hardening creates a distinct hard edge (yakiba) and a softer, more flexible spine (mune).
5. Attention to Detail: Fine attention to detail is often evident in high-quality swords, including precise fittings, intricate engravings, and meticulous polish to reveal the beauty of the blade's grain pattern (hada).
6. Reputation and Authenticity: Swords crafted by renowned swordsmiths, or those following established traditions and historical accuracy, tend to be highly sought after and regarded as top-quality pieces.

It's important to note that the highest quality samurai swords are often handcrafted by skilled swordsmiths using traditional methods, which requires expertise and time. As a result, these swords can be quite expensive and may be considered collector's items or works of art.

If you are seeking the highest quality samurai sword, it is advisable to consult with reputable swordsmiths, experienced collectors, or trusted dealers who specialize in authentic and well-crafted swords. They can guide you in selecting a sword that meets your expectations and requirements.