The comparison between a tachi and a katana in terms of which one is "better" depends on the context, personal preference, and the specific criteria being considered. Both swords have their own unique characteristics and intended uses. Here are some factors to consider:

1. Historical Usage: The tachi and the katana were used in different historical periods and for different purposes. The tachi was commonly used by samurai on horseback during earlier periods of Japanese history, while the katana gained popularity during later periods and was used by samurai both on foot and on horseback. The intended usage and battlefield requirements of each sword varied based on the time period and combat tactics of the era.
2. Blade Design: The tachi typically has a more pronounced curve compared to the katana. This curve was advantageous for mounted combat, allowing for powerful and sweeping strikes from horseback. The katana, with its slightly gentler curve, provided versatility for cutting, slashing, and thrusting techniques in both mounted and on-foot combat.
3. Length and Reach: The tachi often had a longer blade compared to the katana, which provided greater reach and striking power from a mounted position. The longer blade of the tachi could be advantageous for striking opponents from a distance, while the slightly shorter length of the katana allowed for increased maneuverability and versatility in close-quarters combat.
4. Individual Preference: The perception of which sword is "better" can also be influenced by personal preference, cultural significance, or aesthetic appeal. Some individuals may prefer the historical associations and elegance of the tachi, while others may appreciate the popularity and versatility of the katana.

It is important to note that the concept of one sword being universally "better" than the other is subjective and can depend on the specific requirements, combat scenarios, and personal preferences of the wielder. Both the tachi and the katana have their own merits and intended uses based on the historical context and battlefield requirements of their respective eras.