Bosal twin tip is what ive got, its decently loud, sounds down right mean during hard acceleration....kind of like a deep throaty v8-ish tone. full stainless steal, and all that for 389.99 shipped. ive heard the Espilir too, it sound very nice as well. Pretty much any exhaust for the WRX is going to give you a great sound. These are all good brands: Borla, Bosal, Espilir, HKS, Greddy, Perrin, Stromung etc. As for the HKS, ive never heard one in person, but they are supposed to be really loud. BUt i would suspect a great exhaust.