I've read many posts regarding which exhaust system is better than another in regards to horsepower gains but not in reference to complete build quality. What is the preferred exterior metal? Aluminum? Stainless Steel? Ceramic Coated Steel? Also, what about the interior materials such as vermiculite, stainless steel, etc... I want an exhaust system that will not only provide an increase in power but also not discolor, rust or need internal servicing more than once a year. I've heard many pros and cons regarding the aforementioned materials but no definitive answer. Any suggestions?