What is the best renderer out of the ones you have to purchase? I assume it's Renderman since it costs the most, but what is your opinion?
Renderman - $3500
RenderDotC - $595-$2995
Air - $450
Mental Ray - $2,995 or $5,495 + $1000 or $2500 license (since I'd have to purchase it as a stand-alone product)

What is the best renderer out of the free ones?
Aqsis
Pixie
JRMan
Maya's default renderer (free since I obviously already own Maya)

The images I get through Maya are pretty good and I really haven't been able to analyze renders from different renderers to actually see the difference first hand.