cat back or muffler?

I have a 99 a4 2.8 and i want to get a new exhaust system or at least part of it. I have been talking to my friend about it and hes more of a mechanic than me and he suggested that i get a cat back, yet i don't know what is the best kind to get for my car nor what is a good brand. I've done some research and people seem to like the magnaflow 14816 for a muffler. my budgest is pretty limited so i would like to know what you guys think I should do. Going to an exhaust shop and getting a custom exhaust made could be an option too depending on the price.