Comment by amukher1

While I have a personal favorite, I recognize this as one of those question which cannot have one right answer. The best language for the interview is the language in which the candidate is most proficient and expressive in. If you're making the candidate write a lot of algorithms, it helps to have a basic ds/algo library that's flexible and easy to use. C++ has STL, which is great but for people unfamiliar with its style (iterators) or syntactic peculiarities (templates, etc), things may not be very smooth. Java has a decent library too, and I guess so does Python but I'm less familiar.