I'll second everything said here about the AE exhaust I enjoy mine more and more each day. (installed a few weeks ago) I too feel like the car is smoother in power delivery and more responsive too. It takes less throttle input to make the car go. Only issue I have is a vibration transmitted into the car at low rpm. Sounds like a pipe touching something metal or a loose fitting. This weekend I am going to put it up and double check everything.
I'd say the only down side is how much crappier my gas mileage is now cause I am driving the car so much harder to hear it growl.