You should give a look at Turtle Renderer, I have seen good things out of it.

Renderman is a standard, PhotoRealistic Renderman is the renderer that is sold. Its viewed as the best renderer because of its speed and motion blurs mostly.

When you want to pick a renderer, think about what you are going to do with it: stills or animation. In animation you need good motion blurs and speed. In stills its more toward lighting and feature to tweek the image.

Personnaly, I think I will use Maya as long as I can. Especialy since you have unlimited licence with it, this is great for render farms.