Here are some muffler facts. All free flow mufflers give you the same horsepower. Changing out the muffler on a C280 will give you a max of about 2 horsepower. The sound difference comes from materials such as metal thickness and fiberglass packing. Welded mufflers last much much longer than crimped metal mufflers. The best material that will look good for many years is stainless steal.

Here's my experience. I have a single outlet, oval tipped Ractive muffler. Say what you want but it looks damn good and sounds identical to Supersprint on the same car. I have an 18 inch glasspack in front of the muffler to tone down any harsh sounds. The whole system including larger pipe from the catalytic converter back cost me less than 300 dollars.