Vray

This renderer is widely popular for one thing; speed.
Vray offers good control but requires a lot of tweaking until you get a hang of materials and rendering parameters.
Render time is 20 minutes per image, but skilled users can probably get the same result in 10.

Pros:
Top tuned system - if you know how.
Good smooth results with excellent interpolation control.
Support for IES lights.
Good control of anti-aliasing.

Cons:
Tweaking required if you want improved colorbleeding.
Material paramteters are only semi-realistic.
Glossy reflections are extremely slow.