The best thing to do is find a shop that will cut the old one out and let you try a few out before you get one welded in. Not all shops will do that, but ask around and some will. I have the Magnaflow
12226. It's a 14" muffler. The shorter, the louder, and the longer, the quieter. So an 18'' or 22'' are pretty quiet. I just went into the shop and took this one, since it was the only Magnaflow they had. Some older people might consider it sort of loud, but it's just right to me. When you crank it, it growls pretty good. It's pretty quiet at idle, just a really low slight rumble. But once you take off and increase rpms, the rumble grows and gets a nice deeper pitch. As you peak, at say 55mph, it keeps the steady rumble, but quieter than when you are increasing rpms. It's not too bad of a drone with the radio at a moderate level. And after I got it, I had my buddy drive by in my truck to hear it myself and it sounded pretty good. I'd say the sound matches these trucks pretty well. This model is not too quiet, not so loud that it doesn't suit the truck or wakes the neighborhood up, and not like a bumble-bee/ricer honda civic. I've had plenty of good compliments on how it sounds and no negative comments. It sounds a little more "powerful" or "tough."
I would make a video and post it for you, but I don't have a nice camera or anything. So it would sound just like every other youtube exhaust video. Sorry. Best best for you is my first advice. Try to find a shop that will let you hear it on your truck before you buy it, because it's hard to choose one with only the crappy quality of a youtube video.