My son's 90 Mustang has one of the nicest sounds I have ever heard. He has a built 302, full length headers into Flowtech X-pipe, into Flowmaster Mufflers into full length 2 1/2" stainless tailpipes.
I'll have to say, though, that the nicest sounding exhaust note I have ever heard is my friends 347SBF powered Superformance Cobra replica. Those sidepipes are awsome!