As a hobbyist, the only other renderer I have experience with is Pov-Ray mainly due to price.  It's pretty powerful for a freebie, but has a steep learning curve.

The main drawback is that you can't change too much on the models directly in PovRay.  You have to set the models up in Poser, export them, then use PoseRay to convert them (although PoseRay does make it much easier).

It can't import the procedural textures from Poser, but with a little experience, Pov-Ray's scripting language can be very useful.

I'm not sure how the speed compares with other renderers, but the only renders I've had that took more than a few hours either used really large isosurfaces or had things like radiosity count or media samples cranked way up.

It's good to hear others mentioning Pov-Ray.  I was beginning to think I was the only one at Renderosity who used it.