I have Magnaflows on my 67 coupe (289). I knew some people that had flowmasters, but I didn't like them, I'm not totally sure how to describe it, but it didn't sound very full or tuned at all. I am very happy with the magnaflows because they give a great throaty, full sound and they aren't too overly loud. but you can definitely hear it coming. I know some one that has a 66' with a inline 6 motor that sounds pretty good, if I can find out what they have i'll post it. But I vote magnaflows all the way!