I noticed that in the proposal information for OPNFV, that the Linux Foundation will provide the initial tool environment. I don't see any information that specifies what this will look like, or what tools will be used in its composition.
I may be misunderstanding the situation, but I'd say that the ideal build tool to use for the build process would be Gradle. Ant and Maven have been around for a long time, but Gradle was invented to address the shortcomings of both Ant and Maven, although it incorporates the best parts of both Ant and Maven (task library and declarative dependencies).
We can have more detailed discussions about this, but I wanted to get this idea out there if there was any question about what should be done here.