For you I would vote for the slug shotgun for two reasons:
1.) You are familiar with and even have a shotgun. For hogs you don't need a scope or rifled slug barrel. In Louisiana , hog hunting is a short range and fast shooting affair.
2.) A muzzeloading rifle is going to require you to buy one , along with all the accessories, then learn how to load, shoot, and hope you don't need a fast follow up because basically a muzzle loader is a single shot that must be reloaded on the spot without a self contained case.
Hunting with muzzle loaders is a fun and challenging endeavor, but for a one time hunt on a ranch, the shotgun with slugs is the ticket.

Now if you are already a seasoned muzzeloading rifle hunter / shooter then you already know what to do and how to do it...it's just a matter of taking the gun you feel most confident with. I hunt with them and own several that I have taken deer. For hogs , I still prefer having more than one shot..... I can't climb trees too well anymore and hogs can get mean and nasty quick.
Gary