FF can be much better depending on settings. One thing it does well is better render curved surfaces over p4 renderer. You also have more features like raytracing, distance blur, fog, distance fade etc. I use P4 when doing shots that don't require elaborate shadows or accurate curve rendering and use FF for the rest. Also some of the material nodes are not supported in p4 renderer like they are in FF. You can't use displacement maps, for example in p4 and the bump map system works differently.