Poser scenes can be rendered with Vue, Carrara, PovRay, 3Delight (via DAZ Studio) and lot of other renderers. There are some people in the galleries which use Vray or Cinema 4D for rendering, you aren't limited to Firefly.

Every renderer has it's strengths and weaknesses, especially the materials and light options are very different. No matter which renderer you plan to use, an Phil already told you, you will have to learn how to use it to get good results from it.

What kind of images do you want to create? Which problems do you have with Firefly?

A ship in port is safe; but that is not what ships are built for.
Sail out to sea and do new things.
-"Amazing Grace" Hopper

Avatar image of me done by Chidori.