When comparing VRay vs Renderman, the Slant community recommends VRay for most people. In the question“What are the best renderers?” VRay is ranked 2nd while Renderman is ranked 5th. The most important reason people chose VRay is:
It's one of the fastest rendering engine of the "time"
Ranked in these QuestionsQuestion Ranking
Pros
Pro Speed
It's one of the fastest rendering engine of the "time"
Pro Production proven
Pro Support for Blender
See here.
Pro XPU CPU/GPU hybrid renderer
New in version 24. Very fast but not yet feature complete.
Pro Highly flexible
Pro Hollywood standard since the 1990's
Hugely versatile as for every shader can be written in code thus it is extremely fast and complex.
Pro Physically based rendering
RIS and XPU.
Pro Wide feature set
Pro Real-time rendering support
Using interactive rendering RIS/XPU.
Reyes was removed in version 21.
Cons
Con Learning curve
Learning this engine can be tedious sometimes. Specially because you can choose between several indirect lighting (or global illumination) techniques.
Con Very steep learning curve
Users must have a complete understanding of C++ programming to make their own materials.