Things to consider:
- How loud do you want it? (little louder than stock or all the way to ticket-me loud)
- Better sound or better flow? (or both)
- Construction material? (happy with aluminized metal, or want stainless?)
- What type of sound? (classic musclecar or exotic racer)
I personally have the FRPP catback and love it. Stainless steel, made by the OEM supplier (perfect fit), nice low mellow sound, but pleasingly loud on acceleration.
To each his own, and definitely check out mustangexhaust.