I have an X pipe on my GTX, because my exhaust guy put it on! The car does one heck of a burnout and sounds cool as hell!! What more do I need to know???
A lot of good info in this thread, on both sides of the argument. I always thought of it as a sound thing, if you are running a full exhaust system pick the one that sounds good to you. I personally like the sound of an x so that is what I went with, and I don't think it weighs a lot more or costs a lot more than a H or side by side.