You are probably going to get as many answers as there are exhausts with this question.
Different people have different tastes, and it depends what you are looking for.
Personally, I like Corsa and Billy Boat, both for sound and quality. Both have multiple options to satisfy different wants. They have sounds you can listen to on their websites, but they aren't the greatest.
I would also suggest looking up exhaust sound videos on YouTube. There are some decent ones on there. Of course, nothing is better than listening in person.