The MX Master 3S is generally better for ergonomics, especially with prolonged use. Its sculpted design supports your hand better than the Magic Mouse's flatter profile, which can lead to wrist strain for some users. The customization options on the MX Master 3S are also more extensive, allowing you to tailor the mouse to your specific workflow. While the Magic Mouse integrates seamlessly with macOS, the ergonomic advantages of the MX Master 3S often outweigh the benefits of ecosystem loyalty, especially if you're experiencing discomfort.