Depends what you wanted it for? Are you looking to make more horsepower or are you looking for a better exhaust note?
If you are looking for a better exhaust note only you can save some money and just go with a slip on or half system. If you are looking for the whole enchillada then go with a full system. In both cases you should be able to save some weight on the bike.
If you are close to the ocean you may want to look at stainless systems vs aluminum. Carbon Fiber and Titanium will be pricey buy lighter.
That said....Muzzy, Yoshimura, Akropovic