Log4j and Logback are both logging frameworks, while SLF4J is just a logging facade (an abstraction layer). SLF4J is typically used in conjunction with either Log4j or Logback, providing the API for logging while allowing the backend to be swapped without changing application code. Logback is considered more modern and feature-rich than Log4j 1.x but Log4j 2.x has many improvements, including asynchronous logging, making it competitive with Logback. Log4j 2.x and Logback are often chosen for new applications, while Log4j 1.x is considered outdated. In short:

Use SLF4J for a standardized logging interface. Use Logback or Log4j 2.x as the actual logging implementation.