Choosing between Clerk and Supabase Auth for authentication in React and Next.js applications depends on various factors including architecture, budget, and team expertise. Clerk offers a managed authentication-as-a-service platform with an emphasis on developer experience, rapid implementation, and pre-built UI components, which is advantageous for B2B SaaS applications and rapid MVP development. It features automatic security measures and minimal configuration, making it suitable for teams lacking deep security expertise. Supabase Auth, on the other hand, provides a comprehensive backend solution with strong database integration through PostgreSQL, particularly beneficial for applications needing fine-grained authorization. Its open-source nature allows self-hosting, offering flexibility and control, but requires more manual setup and PostgreSQL expertise. Pricing structures differ, with Clerk offering straightforward per-MAU pricing and Supabase bundling authentication with database services, creating complexity in cost comparisons at scale. Both platforms are SOC 2 Type 2 and HIPAA compliant, but Clerk's automatic security features require less configuration effort compared to Supabase, which relies on manual setups for equivalent protection. The optimal choice depends on whether the priority is rapid deployment and ease of use (Clerk) or deep database integration and flexibility (Supabase).