My vote is to start with the Caplock.
As was said, there is much to learn about the Flintlock and even with the help of all of the flintlock shooters on this forum, the path is not always easy.
It is easy on the other hand to buy a Flintlock that isn't set up exactly right from the factory and that can cause the best of Flintlock Shooters to pull their hair out. (Ever notice that they are a little balder than caplock shooters? That's not from the flash in the pan! :: :
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Just kidding, but seriously, there are several reasons the Caplock is a good starting place:
It burns black powder and the substitute powders.
It is historically correct for the late years of the Mountain Fur Trappers.
There were a number of reasons the owners of Flintlocks paid money to convert them into Caplock guns and reliable ignition was one of the main ones. A Caplock isn't real fussy about the caps it uses.
Flints wear out (sometimes rapidly) and are not always easy to find to buy.
Caplocks (IMO) are easier to sell if you decide to because most people don't have the foggiest notion of how to shoot a Flintlock and are cautious about buying one.
Caplocks are easier to shoot well. I say this not because of the "delay" most people expect from a Flintlock, but because it is dam hard to concentrate on the target when there is a small explosion that occurs right in front of your eye before the gun actually fires. Properly set up and primed, the Flintlock is almost as fast as a caplock. If anything is not quite right with a Flintlock, there is anything from a slight noticable delay to nothing but a "flash in the pan".
As for "having a Caplock you will never shoot after you buy a Flintlock", I say balderdash! I own and enjoy shooting both Caplocks and Flintlocks. Each has a place in history, and in my gun cabinet. They both are a hel of a lot more fun than a modern cartridge gun.
I prefer the Caplock for precision shooting and the Flintlock for the challenge of trying to do precision shooting with it and the general fun of shooting it.
By the way, I started with a Flintlock 35 years ago. Although I have no regrets in buying the Flintlock I later bought some Caplocks so you might say I've "walked in both moccasins".
If you can afford just one gun, start with the Caplock, then save your money and buy a Flintlock later. You will enjoy shooting both of them. :imo: