Everyone O know in ML'ing bought theeir first gun & quite promptly found out they wanted something else, because they bought what appealed to them at the time rather than what fit them & was comfortable.
Just recently a guy came by here & tried several dif rifles & owning a Hawken style himself, was simply amazed at the balance or the Lancasters & Isaac Haines rifles in particular. Best way to pik a rifle is go to a big ML shop or a guys house that has a assortment of rifles that you can try them all. This give you some good thinking ammo & the main thing is Looks don't mean nothing if it don't fit you & is not comfortable. Find the style that fits you & you can shoulder well & then look for the gun trimmed out like ya want.
Personally, if I were you I would go with a percussion with a Siler lock & have someone look at it BEFORE ya buy it & be sure it can be easily changed to a Flintlock with simple lock change & vent installation where the drum is. This gives you a lil easier gun to learn with & also you can easily change it for ? $100. or so later.
When you go to get a ML, you need to take someone with ya that really KNOWS them, not bubba dow n the street that shoots skeet or is a rifle deer hunter, you need a real BP guy to be sure you are getting a quality safe gun in good cond.
If you don't own a ML at all & have never owned one, I suggest you go start with a Lyman GPR (Great Plains Rifle) in percussion, then shoot it a while & then if you really like it & want to stay in it you can upgrade from there. You can buy one very reasonable from Midsouth Shooters Supply and get it in kit or complete. I suggest a .54 cal as it is excellent for deer & target & very accurate in the GPR.
This is a small investment & a good starting place for a newbie.
http://www.midsouthshooterssupply.com