Ive always loved the Sound of Flowmaster's, they sound different on the 05+ than previous Stangs but its still a great sound, throaty and aggressive. They are not Too loud like SLP LM's but the chambered design makes them drone a lot around 70 mph in 5th gear, so you either have to drive slower or faster or get back into 4th gear.
Bassani is nice because they are shiney stainless steel but they are More expensive, however i do preffer the sound of Flows to most other axle backs for 05+ unless you run an Off Road mid pipe, chambered mufflers tend to get very raspy.
Flowmaster!!