Polyurethane is the best material. It's flexible and won't crack and it stands up to the most abuse. The ABS plastic is good, but it cracks with a hard enough hit.
Carbon fiber is nice, but it cracks toooo easily, same as fiberglass.
StreetStyler.com is a good source for OE replica parts. They even do package deals on the front, rear, and sides for the OEM Optional kit.