We use Java, so that is what I would recommend.
The first advantage to Java is that it is the language used in the AP Computer Science course, so if your school offers that some students may have Java experience from the class.
Java tends to be more friendly to beginner programmers because of the garbage collection function of the JVM. If you're not familiar with it, it automatically reclaims memory used by objects that no longer have any references to them. This abstracts something complicated like memory management so an inexperienced programmer can focus more on the logic than making sure they don't have any memory leaks. Most FRC applications are probably simple enough that memory leaks aren't an issue, however.
Another advantage to Java (and I believe C++ as well) is dramatically faster deployment times compared to LabVIEW. I spoke to a member from Code Orange, who uses LabVIEW and he said that their deploy times ranged from 5-10 minutes, and I have heard similar stories from other teams. Here I was complaining about 30-45 seconds for Java
The main disadvantage to Java in FRC is that the cRIO JVM is Java ME, which is based on Java 1.3, so doesn't have a bunch of new features like generics.