Hey Z, you first need to decide what you want out of your muzzle loader, You can get close to history with an old style flintlock or a cap lock that shoots round balls or lead bullets, these most of the time you need to get a power measure and measure each shot, they are heavy dirty and obnoxious little critters and at times very uncomfortable to shoot for lack of shoulder pads, they are what muzzle loading season was intended for. Sometimes they misfire, are hard to clean, and smell like skunks and smoke like diesels when you fire them. If you are out for the old fashion hunting experience then these are the way to go, they are fun and challenging to shoot, Thompson Center makes good ones there are many good ones that name just jumps off of my head. I would recommend a 50 cal. If you just want to hunt deer and basically extend the deer gun season, then you can go with the Newer inline muzzleloaders, they mostly but not always use shotgun primers for the ignition system and is close to 90% or better. the newer ones are chambered for special muzzleloading bullets that are alot closer to rifles than muzzleloaders, they have premeasured power pellets, that you just insert into the barrel, cleaner shooting, the bullets are pretty good, they mushroom well and fly straighter. In an inline I would recommend a 45 cal. you can shoot them at over 2200fps, they really are muzzleloading rifles. It is purely a matter of taste and what you want out of your rifle.
note .. this reply is just one mans opinion and is not intended to be an attack on anyones style of muzzleload hunting. There is no implication of old style muzzleloading being more sportsman like than anyother method of hunting, nor is there any implication that the new style rifle muzzleloaders are any better than any other form of hunting .. Hunting is a sport and how you choose to persue that sport is entirely up to the indivual. Gee you think I have read all the arguing over bow/crossbow hunting