The first thing to look at is the size of the muffler. As a general rule of thumb, the larger the muffler the quieter the sound. Here are a few examples of what I commonly install on the Rebel.
Magnaflow - The Magnaflow is a well made performance muffler. In my opinion it sounds similar to a European V8 and it's probably the most tame sounding of the group. If you want a little more aggressive sound than stock but don't want any
or very little drone in the cab, this is a great option. You can purchase this muffler with a single in and dual out, so you won't need a Y pipe. I'm in Southern California where costs are probably higher than most places in the country (got to pay $20K a month for the shop), and I typically charge around $225 for this muffler installed. This muffler usually won't piss off the neighbors.
Carven - In my opinion the Carven is a great sounding performance muffler. They have a deep tone at idle, a mild tone when cruising, and they sound like a bat out of **** when you step on the gas. Carven makes two mufflers, the "R" and "TR." If you go onto Carven's website, you will see that they have two bolt in systems for the Rebel. The direct fit "Progressive series," which is a "TR" muffler with a Y pipe attached and the "Competitor series," which is a "R" muffler with a Y pipe attached. They both have a similar sound but the competitor is louder (smaller muffler). At my shop, I make a custom Y pipe and extend it 1' past the muffler, which I have found slightly reduces any drone (I found this out by accident). With the "TR" there is a very small amount of drone when the truck is in ECO between 58-62 mph. It is very minimal and I hardly notice it. I unfortunately can't say how much drone the "R" has because I haven't driven one for any length of time. I will say that the majority of my customers are very happy with the "TR." I have had a couple customers come back saying that the "R" was too loud. I typically charge between $300 - 325 for the muffler and custom Y pipe installed. (Remember I'm in SoCal, it's expensive here). Your neighbors are probably going to hear it when you start the truck. The initial rumble is awesome. Coming home you can keep the noise pretty low as long as you don't rev it.
Flowmaster - The Flowmaster is another great sounding aggressive sounding muffler, although except for the Outlaw they usually don't do anything for performance. The Outlaw (which will require a Y pipe), and the 10 Series (no Y pipe needed, single in dual out) are very aggressive sounding. They sound great at idle and when you step on the gas. While in ECO mode, you may experience some moderate drone throughout the RPM range. The 40 Series is another common Flowmaster for these trucks. It isn't as aggressive sounding as the Outlaw or 10 Series. It also has a nice deep tone at idle and throughout the power band. It may still have a little drone in the cab. I install Flowmasters on the rebel for between $200 - 225. The Outlaw is a little more, due to the Y pipe, priced similar to the Carven mufflers.
I know there are quite a few other mufflers out there but these are my most common installs. They all sound great depending on what you are looking for. If you're over 50, go with the Magnaflow. If you're between 30-50 go with the Carven. If you're in your 20's, Flowmaster. Good Luck, I hope this helps you!