Hey buddy. An H-pipe has that classic rumble that everyone has, an x-pipe has a more high pitched throaty sound. I believe the x-pipes also give you a little more power. I prefer the x-pipe becuase it sounds wicked and different. you can go to
mustangexhaust.com to listen sound clips.
my bro got the magnaflow x, (with frpp ceramic headers and ameri. thunder flowmaster catback)
and the stock h vs the mag x was night and difference. It changed the entire pitch of the car. It's got this seriously wicked growl to it. It is still distinctly american and deep, but it's got a wicked hi tech sound to it to (hard to explain) I'd buy one in a second if I had the cash.