I like to hear the exhaust note over the propeller... Cat's you can hear each cylinder... when you attenuate the exhaust note, the propeller noise goes into resonance with the engine exhaust, and you loose that distinctive alternating exhaust sound... I dislike the sound of the OS FF-320 for that very reason.
My ft160 exhaust on the j3 is 2 into 1 (1" expansion chamber), without any internal baffles, with a large exit pipe... its not as loud as cat's, but you can still hear each cylinder over the propeller noise... but both the160 & 320 are quiet engines anyways with the sock pipes.
It is personal perference, as long as you like it, is all that matters.