When I was looking at exhausts I narrowed it down between a Magnaflow and a MBRP. I heard some people say the magnaflow didnt fit correctly and rusted faster so I went with a MBRP 4in stainless.
IMO I'd get a stainless 4 before I bought a 5 so it wouldnt rust and last more than a few years. The big killer in exhausts is the cat. If you eliminate that then you will get alot more HP and noise from the motor and turbo.
So to answer your question Id get a down pipe back exhaust. Alot more power and alot more noise.