After reading numerous threads and listening to sound clips on YouTube I decided on Khrome Werks 3 HP+ tapered mufflers. I just installed them along with a Stage 1 air filter kit and a V&H Fuel Pack on my 2010 FXDC.

Installation was a breeze (the FP is kind of a pain to place). Just took her for a 30 mile trip; here is the verdict:

Bike runs great, definitely more bottom end torque and strong midrange, no decell popping. The sound has to be the deepest there is, it is almost like a subwoofer where you can feel the bass, no tinny sound at all. I used to have a RK with Rinehart's that weren't near as deep.

If there is a drawback, it is a little louder than I expected when you open her up.

 

Don't worry about the extra noise. You will get hearing damage soon and it won't be a problem after that.

You may find after you have ridden with the Fuelpak a bit longer that its no longer so good at low revs and cruising speed, you might also get some decel popping. The downside to Fuelpaks is that the O2 sensors are retained and they, along with the ECU, pull the air/fuel ratio back down towards stock after a little while.