The best "cat-back" exhaust

[Mr 5 0]

I have the DynoMax Super Turbo catback system and found it to be good quality and a nice, mellow sound; but the 'sound issue' is totally subjective and also dependent on the H-pipe configuration and choice (or absence of) headers.

No cats/headers will make any cat-back system louder and factory cats & headers will make it quieter (and more restrictive).

Borla is a very high quality manufacturer but you pay for that quality, of course.
Flow Master is generally loud but decent quality but as a previous post mentioned, you won't see more than a few HP gain with just mufflers and pipes - you need the headers and H-pipes replaced to get a real power increase, simply because the factory mufflers/pipes are not that restrictive but the (4-cat) H-pipe is, as are the headers, although they don't rob as much from a stock engine as they would on a modified Mustang.

To answer your question: I recommend Walker DynoMax as the best for the buck.