Some people think that a raw, unmuffled sound is best. Other people want a more restrained, tuned note. So, ,"best sounding" is pretty broadly subjective. I liked the Borla muffler system because it was sporty sounding like an improved touring road racing car without being too harsh .
The Ford Racing/performance cat back system is a little louder/rougher than the Borla system.
You can hear a lot of the sound clips of various brands by searching for performance exhaust systems on YouTube and make a decision about the best one for you.