From what I understand, and I am still pretty new at this, the "X" pipe gives you a more harsh raspy sound wile the "H" pipe gives you a smoother mellow sound. There are probabaly some performance differences in them as well but I havn't read that far yet. Any of the good quality exhaust makes will probababaly give you the same results regardless of who you go with so I really do think it is more a personal preference. You should listen to some vidoes on Youtube, lol.