I think that I've tried just about all the various options and so far find the OBJ format to work the best. However, when I export by materials, which makes sense, ALL the AC geometry of that material comes in as ONE single polygon object in C4D. This is a major, major pain as there is no easy way to split all the polygons like the explode command in autocad...you have to do it polygon by polygon. What I would really like to see in the file transfer is all the polys of one material to come in under a single null object in C4D so that each part is easily accessed amd edited in C4D and yet comes in already "sorted" by material under the null object. This would save a lot of time. By the way, that is the way FormZ objects come in, except I used to do it by layers, but same concept.
Have I missed an option here somewhere that might work better? I did try the AC to C4D exchange plugin...and offhand can not remember the results as far as how the geometry came in.