Another quick thought
"Best" needs to be understood in one of 2 ways.

#1 The best quality of any gun made in the muzzleloader era, (from the days of the hand cannon to the beginning of the breach-loading era) or any reproduction of any such gun. Quality being viewed on the basis of accuracy, dependability and artworks

Or #2 The best technology ever made (so far) for the use of killing game with a weapon that happens loads from the muzzle.

In category #1 I would say the ones that probably are on top of the heap were the German and English guns made in the late 1860s
In category #2 I have to say.................I don't know. I have no interest in a muzzleloading rifle made with 2017 technology. I have a scoped AR-15 in 6.8 SPC now. If I only carry one round in the chamber and no magazine on my person I would have the same capabilities as such a gun, but hunting that way seems to beg a question to me.

Why?

I don't care what others hunt with.

But when I hunt with a bow I want to hunt the old way. Long bow with wood arrows. Same with any muzzleloader. My rifles are recreations of guns made in the late 1700s

I can kill game easier and farther away with my 270, or my FN-FAL, or my Ruger SR762.
But that's not the point of hunting with a weapon that provides a greater challenge.

When I hunt with my long bow, or my flintlock I hunt in the regular season. I never bother with "bow season" or 'muzzleloader season".
I am not trying to cheat. I am not even 100% dedicated to killing an animal. If I were I'd be using one of my auto-loaders.