Short answer: either one works fine on an RC51.
Just doing some basic research for you - the VX2 and ZVM-X in 520 pitch are very similar in specification. The ZVM-X is heavier and stronger, although the wear rates are the same. I would imagine the ZVM-X will last longer based on the tensile strength (think of two forces pulling apart).
I also highlighted the ERV3, which a lot of people opt for around here. It's even lighter than the VX2 (barely), but is stronger and will theoretically wear out faster.
Fwiw, I run the 520ZVM-X on my bike for the mileage. I didn't go with the 530 pitch for the weight savings.