IF you look at them the xs are more of a turbo style muffler. the stinger catback has just a round muffler.
The stinger is louder it is their answer to a glaspack type exhasut like magnaflow has is my guess. magnaflow has its magnapack exahust that is louder.
borla has its turbo style cat back and the stinger.
IF you keep cats on the car get the stinger. If you remove the cats only get the stinger if you really like loud.
The turbo's sound great once the cats are gone but I was not happy with the cats on. then agian 4 cats will make the car fairly quiet even without muffelrs.