The problem with your request is that everybody has a different interpretation of what "quiet", "good", and "bad" are.
You're told to search, yet in most of the threads I've read, the idea is to make the car louder than stock, not as quiet as stock.
And while *describing* the sound is not easy for most, most don't even try, so you're still in the dark.
I think your best bet is to just shop a few muffler shops and ask the price and then ask them a lot of questions. Sure there in the business to sell stuff, but I've found that most of the indies are pretty fair, and if two or four shops give you similar answers, then you're probably onto something.
When I put low-restriction mufflers on my Z/28, a local guy suggested Walker Turbo Mufflers. They were pretty quite, I got a couple more MPG, and under hard acceleration they had a bit of a growl, but not much. My unsilenced air cleaner made more noise.
And personally, if a car alleges high performace with it's exhaust, I think it ought to back it up. No sense in a car posing. That's totally rice. (Not that there's anything wrong with that.) You may as well hang your head out the window and go "Vroom, Vrooooom!"
Any car can go fast, eventually. It's the 0-Fast that counts. And a quiet car will at least give a better *impression* of performace.
