FLOWMASTER. Do not put anything other than a single chamber Flowmasters on your Mustang. Anything else will sound like crap in comparison. There is a reason why an overwhelming majority of Mustangs made since 1979 all have Flowmaster mufflers.
My exhaust set up on my 96 gt is hooker LT headers, O/R X-pipe and slp's. I had the flowmasters on with set up and sounded like complete ***(raspy as hell!), switched to magnapacks and it made it have a deep tone(no rasp)but didnt seem to loud so i switched to slp's(tiny bit raspy) and wasnt as deep(still pretty deep tho) but def louder at WOT.
Mike is right,the Flows will give you a real raspy tone and they also drone @ highway speed.I run a Mac O/R prochamber and a Mac S/S catback on my 04 GT.Love that sound!!No rasp at all,nice deep rumble @ idle,almost like a burbling sound @ idle and when you mash your right foot to the floor,the sound of power,I love that sound.I always get compliments from other Mustang owners when I take my GT out for a ride.One of my gearhead friends have the SLP L/M 2 on his GT,they sound really nice,no rice here,just power.Go to you tube,type in Mustang exhaust in the search box.You'll find every exhaust system people have installed in there cars.You can hear and get an idea of what each system sounds like before you spend any $$ on it.Check it out.Hope this helped.
If you want a sound that is wicked and sounds unlike every other mustang with flowmasters that go with bassani. slps sound ok but are very loud, I think they sound more like straight pipes on old mud trucks.