If you are using V-Ray version lower than 3.1, be aware that the materials in the BRDF section use Microfacet GTR (GGX). If your version is older than 3.1, the BRDF field will be empty. Choose Blinn, Phong, or Ward – whichever is preferable for you.

For Corona render, it is recommended to use version no lower than 1.5, as the glossiness of materials is configured with PBR in mind.