There is no Number 1 🥇, Make your Own research and try to find the perfect system for your next project
1: Firebase Authentication
You can use Firebase Authentication to allow users to sign in to your app using one or more sign-in methods, including email address and password sign-in, and federated identity providers such as Google Sign-in and Facebook Login.
2: Auth0
Auth0 is a flexible, drop-in solution to add authentication and authorization services to your applications.
3: SuperTokens
it is an Open-Source auth provider Add secure login and session management to your apps. SDKs available for popular languages and front-end frameworks e.g. Node.js, Go, Python, React.js, React Native, Vanilla JS, etc.
4: NextAuth.js
NextAuth.js is a complete open-source authentication solution for Next.js applications.
5: Breeze & Next.js
Laravel Breeze can also scaffold an authentication API that is ready to authenticate modern JavaScript applications.