I don't know anything about the first two, but I know that having an x-pipe will make the exhaust note lower in volume because the pressure waves have a chance to cancel each other out. I came up on this subject a few weeks ago when i was looking to buy real twice pipes for my 280. when you isolate the cylinders from one another it is much louder and chainsaw-like (hondas, for example) . I'm assuming you have a v-8... if that is the case, for sound, I would go with x-pipes. I don't konw how this affects performance but the twice pipes system for the l-28 is supposed to be the best flowing when taken straight from the headers as 3-2 and out. Hope that helps!