Bosal and Magnaflow are the two quietest I've heard. Bosal is the quietest of the two but i really like the tone the Magnaflow gives off. You can even get a second resonator spliced into a magnaflow to make it super stealthy.
If you really want a Hi-Flow exhaust, get 2.5 or 3 inch. Most don't recoment it unless your getting boosted, because it lowers your backpressure alot. Focus Central Uses a 2.5 inch on there 200+ N/A focus I believe. YoDude Exhausts