My truck had 40 series mufflers on it, and they were way too loud for me (and my neighbors). I ended up going with 50 series Delta Flow. They're fairly mellow at idle, but they make decent noise when accelerating hard. The aggressiveness of your camshaft will have a big impact on how the exhaust sounds.
Here's a good comparison video of the various types of Flowmaster mufflers.
https://youtu.be/JcqJmwaDfYE?feature=shared