What is the strongest katana in real life?

Could you please elaborate on what constitutes the strongest katana in real life? Are we considering factors such as durability, sharpness, balance, or perhaps even historical significance? Are there any particular katanas that stand out in these aspects, and if so, what makes them so exceptional? I'm curious to learn more about the criteria used to determine the strength of a katana and the specific examples that embody these qualities.