When it comes to aftermarket exhaust systems for your Harley-Davidson, you have two main choices: a slip-on Harley muffler system or a full system. Slip-on systems are usually less expensive than full systems, and they're also easier to install since you don't have to remove the entire stock exhaust system. However, slip-ons don't typically offer a performance increase like a full system would, they just make the bike louder. Full Harley-Davidson exhaust systems offer the best performance gains, but they're also the most expensive and difficult to install. If you're not comfortable working on your bike, then it's probably best to leave the installation to a professional.