RE: 3-9 or 2-7 or 1.5-6 power scope for muzzle loader?
I like the NIkon Prostaff 2-7. It give me the nice wide field of view for close shots and enough mag for the longer shots (long for a ML). And IMO it looks sleeker on a ML than a bigger 40mm objective.
And its clear. Now if you want the best of both worlds, you can go with the Burris Short Mag scope in 3-9x32. It will cost you more. But they are good scopes.