Before this is closed for "not being a good question", I'll get some comments in.
You might want to learn the same thing that most other developers want to learn. Look at the third slide of the following slideware, which shows the results of Zeroturnaround's yearly developer survey. For this set of >2k developers, when asked what technologies they were interested in learning, Gradle was at the top of the list.
You can use either Maven or Gradle to build projects using Spring or Hibernate, but it's useful to point out that both the Spring and Hibernate code bases (not necessarily the applications using them) use Gradle to build their deliverables.
Maven provided the best build solution for quite a few years, but it's difficult to customize a build, and most Maven build scripts are very "noisy". Gradle solves those problems, while providing a smooth migration path from Maven or even Ant.