This is like asking who makes the best speakers, you will get 1 million opinions all different. Everyone hears differently and wants different things from their exhaust. I can say that you likely wont notice any performance difference between any of these systems (as long as they are the same size) although they would like to claim otherwise. It comes down to sound which the site mentioned above is great for, and that is BY FAR your best bet. That said more expensive exhausts I have noticed, eliminate the idle drone that makes your brain hurt when you are sitting at a traffic light. For example I had a Corsa on my C5 that was great, nice quiet rumble at idle, and then ripped open at full tilt. In contrast IMO Flowmasters sound like crap, they are a cheap exhaust that is way too loud and droney, and not a tuned sound just a loud for the sake of being loud sound.
Like I said, listen to as many as you can then make your decision.
2010 Chevrolet Camaro SS - Daily Driver
2008 Chevy Silverado 2500 HD LT 6.0 - Tow Vehicle
1995 Volkswagen Golf Race Car
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