JOHN16V:
Depends what you are after here. If you are looking to put a down pipe on you need to pay attention to what you get. Some cat backs do not fit with some downpipes.
If you are just looking at a cat back I have been told that the Greddy is very quiet. But it does have some fitment issues and apperintly it hits the Diff carrier. As for the Borla I have not heard much on that one.
Matt