Well, probably percussion to start. I would suggest looking for a decent used CVA or Traditions gun to start. If you can find a decent Thompson center Hawken or Renegade for cheap, that would be better. I have bought a few for under $150 locally, however, they typically go for much more if folks know what they are worth.
How much do you want to spend. Cheap will get you started but may not satisfy you if you like the finer things in life.
What time frame are you interested in if that matters to you. A rifle from1740 is very different from one from 1840. What are your primary goals, very small groups will demand better sights than what originals from the 1700's had.
What powder do you plan on burning, The holy black will work in most everything, pyrodex and 777 will work better in a percussion gun.
Sit down with yourself and a piece of paper (I am serious about this) and write down what your ideal rifle would be and what you see yourself doing with it. This will keep you from getting buyers remorse two weeks after you get a rifle and say....I really should have bought the other one.
And if your like the rest of us, a year or two from now you will have bought several to cover all the bases.
@KCode98, you need to decide on how much you want to spend. Do you want a rifle to learn a bit about shooting a traditional muzzle loading rifle? Are you concerned about having a historically representative rifle? Tell us more about the purpose behind your desire for a traditional muzzle loading rifle.
A Tennessee styled rifle would be a good rifle. Used ones are available fairly often and can be found in percussion locks or flint lock versions. For a first rifle, the percussion lock version will be the easiest to become proficient. A specific brand isn't necessary to specify.
So what's your budget is a good question for you to figure out. You're going to spend more for a factory made "historic repro" than for a very viable and less expensive civilian caplock from a factory. Of course a semi-custom or completely custom rifle will usually cost the most.
The Military repros are durable, tend to be very accurate, and will hammer deer.
They are expensive, and use a very large ball or even heavier conical bullet, so they will kick a lot, compared to repro civilian rifles.
The civilian repros also tend to be very accurate, will hammer deer, and especially when using round ball, they will have less recoil. They also cost less while giving good quality. Lyman Great Plains Rifle : Percussion is a good choice for a budget. It's a "plains rifle" style, so sorta from the era between the beginning of caplocks to the Civil War.
So is the Pedersoli Frontier Percussion, walnut stock, Rifle. This is a full stock longrifle, which would've been used in the states East of the Mississippi from the dawn of the caplocks prior to the Civil War up to even the 20th century and The Great Depression.
You should also note that both of the above rifles will shoot a heavier conical bullet if you are concerned with taking a boar, or get a chance to go out west for Elk. For deer or targets, round ball works fine in them.
ANY of the above choices will give you, the end user, a very good muzzleloading rifle.
My first muzzleloading rifle was a navy arms Remington zuave rifle musket, which I bought new for all of $ 89.00. That was a long time ago, last time I checked the same gun cost $ 1000.00 or more. I will say this, I could drive tacks with that rifle. I wish I still owned it.
Although it was modeled on the 4th model Enfield and would have therefore missed use in the Civil war , I would look for a Parker Hale Enfield . I think it's a better musket and was close enough to Civil war era to suit me if I was in the market . They are not cheap but they are as good as it gets . Check out this link.