Whats the best exhaust?

[Rollinastang]

I got an 03 convertible v6 automatic. just put a K&N intake on it last summer. when i have the car in park or neutral and rev the motor there is a slight sound when i let off the gas as if it's not releasing the exhaust fast enough, also when i shut her down there is that same sound.
First question is will a cat back dual exhaust fix that stupid sound or should i take it too the shop, this noise didnt happen until i put on the air intake so i am assuming i need a better exhaust. and what brand is the best i want a deep sound all the way around not just at heavy acceleration.When the car is idiling i want it to be heard you know what i mean?
Alot of people i talked to online say flowmaters are good enough but i am kinda stuck on Borla. There is a quite large price differance between the 2 and i dont wanna spend more money if they both are gonna sound the same in the long run. Also what about MAC or Bassani i havent heard too much about them but i seen them? Reminded i have to keep it emission legal so off road pipes are no option.
Thanks for your help!

[StrokedStang]

I have a preference for MAC myself!!!

[Orange97GTVert]

I thought I had responded to this post once, but I don't see it, so I will post it again. The sound you hear, does it sound like it is exhaling when you turn the engine off? If so, that is your Cold Air Intake. We put one on our 02 V6, did the same thing. Changing your exhaust will NOT change this noise at all. Of course, exhaust changes are cool, so by all means do it. I would go for an H pipe or X pipe with cats if you live where they do sniffer tests, and then you can use a catback for the GT's and get true duals. Flowmaster 40's are nice, but tend to drone pretty bad on automatics. Haven't heard them on a V6 with true duals though.