I've ran a few different set-ups on my Impreza, (most recently running stock, now Prodrive)... The Prodrive exhaust was BY FAR the best sounding axel-back I've had on my car or heard.
Its smooth at idle, but accentuates the rally car tone. Do a search, and you'll see that this is the exhaust to get. If you're looking for something loud, this isn't it. It's actually quieter at idle than stock, but gives the rally burbles when cruising and coming on/off the gas. You wont' be sorry installing this exhaust. I've had mine for about a month, and I gratuitously drive around with my windows down just to hear my car now