Choosing the right identifier format is crucial for your application's scalability, performance and maintainability. This guide compares GUID/UUID v4, GUID/UUID v7, ULID, KSUID, SnowflakeID, NanoID, Cuid2 and XID to help you make an informed decision. For the safest, standards-based choice, use GUID v4 (fully random) or GUID v7 (time-ordered for databases).