The biggest difference is weight and quality.

The Volks are going to be lighter, and they *are* stronger. But you have to decide if the extra 2 or 3lbs (or rather, less 2-3lbs) is worth the extra $1500 you'll spend for the Volks, compared to the $600 you'll spend for the Rota's.

I think most people will say that Knock Off's are terrible, and in most cases they are. Rota's however, are a good quality wheel, that is lightweight (not AS light as a Volk, but pretty damn close) and still very strong. I beat the hell out of my Rota Subzeros (CP035 Replicas) and even got flat tires and stuff, and never had a single bent rim. Some people have had issues here or there, but the same can be said for any non-super high quality wheel.

17", at 16.8lbs, strong and looking great, at ~$110/wheel -- you can't really go wrong. Go with Rota's.

Color wise, the colors are going to be off a tad bit. The Gun Metal is a little bit darker on the Rota's, and the Bronze is a little more brown, but they're still excellent looking finishes on the wheels.