I know gradle, and pretty well at that. I had to learn the basics of maven to develop a Jenkins plugin (at work). Developing jenkins plugins for a long time required using maven. Now there's the option for using gradle, but my recollection was that it was a sub-par experience.
Afaict, everything just relies on Maven and its packages as the backbone. At least, after any sort of Java-dev activity I risk discovering 1.5 GB of Maven's package cache in my home dir.
