This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Note that all of these 3 projects have the same primary author. But the latter 2 were created to correct issues in the former. There is no reason to continue using log4j (no longer under active development) on any new projects.
Also sl4j is a logging abstraction layer it is not a logging framework, it is used together with a logging framework (like logback or log4j).