its not which one you choose. the mazdaspeed 6 is just one of the hardest turbo cars out there to swap a dp. You can go with any brand you want to, but it is still going to be a bit*h to install. The pre cats are too big to fit easialy out of the top and the bend that goes to the turbo is to big to fit out of the bottom, so you have to move your engine around a bit to get the first pre cat out of the top of the engine bay. that is probably the worst part of the install...everything else is just getting off bolts that have fused on, and unscrewing bolts you cant see..ya just need a lot of patience