Flowmaster 40 equals loud, tinny sound under accelleration with considerable interior resonance at 2000 rpm and considerable interior noise the rest of the time. Go to the Flowmaster web site for comparison audio of their different muffler types.
Dynomoaxx depends on which one you get. Their basic entry level turbo is similar to all other turbo mufflers, throaty at idle, kinda loud under power, mild interior noise.
I have no personal experience with the others.