this is maybe best answered with what do YOU like shooting more?
IMO< if me, I would go with the shotgun, for the simple reason being this, a faster second shot IF needed, NO smoke(then again you can use powders that don't smoke like black horn 209 or likes)
but a shotgun is easier to load, unload, and less cleaning needed!
BUT NOT all shotguns are the same quality when shooting slugs, some can be real tack drivers as well
I had a TC encore and hunted many states where its either a muzzleloader or a shotgun deal on deer, and have used both, I spent a LOT of money on some better shooting guns of both types and still prefer shooting the shotgun I have now for slugs( a custom built rem 11/87)
its got less recoil, shoots very well , loads unloads fast and easy
HOWEVER, I will agree, that there are better inlines and likes for longer shooting if that is your goal
some of the smokeless powder muzzleloaders come to mind here, or a custom long range one made to handle extra hot charges to reach farther out
but for me, when I hunted things, I wasn't trying to shoot far with things, minus at a range on paper where I did get out to 300 yards with both., again on paper and even a tad farther, but I still wouldn't take shots at deer past my ,
and mean " MY " comfort lever with either weapon past 150 yards!
others might feel differently, but for me the shotgun gets my vote
and keep in mind, there are some shotguns made for slugs that shoot VERY well when you find a load they like, bullet drop scopes to get you on target from 0-150+ yards too, JUST like there are better muzzleoaders and scopes for them
so really comes down to what YOU prefer!