For students who are already "into" programming, Java is probably the most reasonable option for FRC. For students who are just getting into it, LabVIEW is by far
- the easiest to start with
- the best for having multiple people looking at the code simultaneously
- the fastest for implementing parallel tasks
(all in my opinion, of course).
The important thing to keep in mind is that whatever they learn now very likely won't be what they use in the "real world". With that as a guiding principle, I would suggest choosing something unlike what they already might know, on the theory that it's always good to have multiple viewpoints when approaching a task.