When I got my Fat Bob in 2013, I went the cheap route and stuck a set of Screamin' Eagle slip-on mufflers. They are quiet, but make a good rumble when you throttle on. I like 'em, and wouldn't think of changing except for one little detail.
The first thing to touch down is the very tip end of the lowest muffler when aggressively ripping through curvy pavement, mountain riding, etc. I'm looking to go with V&H shortshots, not because of the sound, but so I have more lean angle on the right side. I'd prefer to go with a good 2-1 exhaust system that sits a little higher up.
Anyway, good luck to you and I'd love to see what you decided on.
Ride In Peace, Rick "Rubberdown" Massey
Ride Forever Free, Larry Weaver