[idunno246]

This doesnt discuss things like, which backend did they use for slf4j. Also, concurrency should have a huge affect, as log4j has some locks in it, and iirc log4j2's main claim over logback is in speed in concurrent environments.

Really, you should always use slf4j, because all your libraries will be a mix of log4j, JUL, commons logging, etc, and slf4j will give you control over them all. It also comes with features some(log4j) of these dont have natively, like passing objects in args to do printf style replacement only when the log will be printed, instead of concatenation that always happens. Then use whatever backend you prefer, probably logback.