The last I had checked, in terms of absolute reduction of sound, the Walker quiet flows were the quietest tested. Obviously no test will include all available mufflers, but the test I recall it was run against Borla and the like, and still came out ahead.
I have yet to install mine. I dislike the flow master 10 series on the truck now at any speed, but I'd rather hear nothing too, and I know the flowmaster design is not for someone like me. Except when free and falls into my lap right when I need it.