Best exhaust kit for sound:
347 stroker
AFR 185s
Monster camshaft
Holley Systemax II intake
Adam
Amen. The exhaust only sounds as good as the engine you put in front of it. If you are really going for that trailer park sound, buy a set of Flowbastards. It's really going to put a damper on your performance though. If you want to be the social outcast of your group of friends, buy anything SLP. If you are serious about your Mustang, want it to sound good, and care about performance, buy a straight through muffler, like a Dynomax or Magnaflow. It's an easy test, go pick up the muffler, and drop your keys into the inlet. If they fall out the bottom, buy the muffler and drive home. If they get lost in the muffler, call a tow truck, and shop elsewhere.
Kurt