Third party renderers is a big discussion. Lots of people like one or another, lots like VRay, Arnold and Octane I haven’t tried any of of them but have tried the demo’s of Maxwell, Thea, Indigo, Cycles and lately Corona. I like Corona a lot as it seems to be the best at integrating with C4D, at least for me and very nice results (I think). Since I’m on the Mac right now Corona is free as it’s in testing for Mac but it’s very stable. They say Team Render is coming it’s not there yet… and Corona is a CPU renderer as well (but faster than Standard and Physical for GI type renders) most of those others are GPU only or a combo of CPU/GPU. I would recommend trying demos of as many as will run on your system or you like the look of or can afford as some are more pricey… and since all the renderers out there fit into the C4D workflow differently and all have their own material system, you have to find what works for you.