self explanitory. just need to know why one is better than the other

 

Because with a catback you are only getting just that. Usually 3" piping starting at the cat, to the muffler. But witha turboback you get a full 3" exhuast system including a downpipe, new cat (or test pipe removing cat) and complete catback exhuast. So youll have better HP gains from a turboback because you now have more areas for air to flow with a 3" pipe as opposed to a 2.5"

 

I agree with John. Plus if you upgrade your turbo it is very important. If you put more air in, you have to let more exhaust out to realize the full benefit.