In my opinion, the most important feature in a passwordless login client is strong and secure authentication because the main goal of passwordless systems is to improve security while making access easier for users. Features such as biometric authentication, passkeys, or multi-device verification help reduce risks like password theft, phishing, and credential reuse while also simplifying the login process. A secure authentication system can provide faster access without forcing users to remember complex passwords, improving both convenience and protection. While usability, cross-platform compatibility, and easy integration are also valuable, strong authentication has the biggest impact because it directly influences both account security and overall user trust.