I have Flowmasters on my Camaro. They sound wicked, are loud, and flow like garbage. Probably one of the worst flowing mufflers out there, but I have electric cutouts to aid in the flow dept.
Putting Borla XR-1s on our Chevelle. 3 inch with a stainless X pipe, and tailpipes to he bumper. Heard that combo at GG autocross on a DSE car and was hooked.
I have also had good luck with Magnaflows and Dynomax race magnums in the oval case series of each. They are quiet and flow air like mad.
My favorite combo so far has been on my Nova though. 3 inch pipe to the bumper, stainless x pipe, and race magnum bullets. It was loud but very streetable and I always got compliments on it.
https://www.youtube.com/watch?v=w0dL_VBNqEI