If you are only going to use for muzzleloading:

T/C Omega .50 stainless
Knight Disc Elite .50 stainless
Knight Revolution .50 stainless

If you think there is the possibility of muzzleloading + other tpyes of hunting/shooting:

T/C Encore 209x50 w/ the ability to switch barrels to centerfire or shotgun would be a hands down choice.

Strictly for ML'ing, I personally think the Omega or Disc Elite are the way to go right now. You surely wouldn't go wrong with either one of them!

Good luck!