I've seen some really good quality smoothbores (both flint and percussion), AND exceptional shooters that can outshoot many people who use a rifle at 100yds. That is not what you should expect from getting started though. It's just that it IS possible to do...
Most smoothbores either don't have sights or may only have a small blade or bead front sight to provide a basic pointer to better aim the gun. If the gun is of the suitable style, it's possible to use the slot in the screw that goes through the tang of the barrel as a "pseudo rear sight", or you can put sights on a gun... it's just that if we are being true to the designs of the originals, we may have to shoot without sights.
A rifle can easily increase the "effective range" of a gun by a factor of anywhere from 2 - 20 times greater. The higher multiplier number comes into play when using elongated conical bullets, instead of a patched round balls. Don't bother trying to shoot any bullets out of a smoothbore, they go out of kilter after they leave the barrel and tumble uncontrollably. Rifling does improve accuracy by better stabilizing the bullets--which in turn gives them a longer effective range.
For whitetail deer hunting in the heavy cover (such as where I mostly hunt)--there is no great superiority or advantage to using a rifle. I rarely get shots over 40yds, and 25-30yds is a typical shot. The ball that is "not spinning" from the smoothbore might shoot just as well as the "spinning" ball from the rifle at these ranges.
Typically being traditional muzzleloaders, we like to use patched round balls as the preferred projectiles. Have you ever shot a flintlock before? How about a muzzleloader of any kind? Ever shoot any modern guns?
Percussion guns may not be inherently more accurate, but if the powder flare of the flintlock (and the delay) distracts your hold, aim, concentration, and follow through; then you should maybe select a nice percussion gun instead.
This being a "first" muzzleloader, I would look for a nice used gun, you might decide that you do NOT like the "retro" challenge of a muzzleloading gun. I doubt you want to spend a pile of loot--just to "find out". Traditional styled muzzleloaders are getting harder and harder to find as factory made gun choices are fewer adn fewer. There are also custom builders/makers--but that's when you get into the "$1200 plus" guns.
What particular gun do you have in mind? How much are you willing to spend to get started? Remember that there are a lot of "possibles" out there to buy, but you won't need all of them to get started for "trying out".
Now I've probably confused you more than a "dog staring at a porcelin cat", but I did want to give you some things to think about.
also with kind regards,
WV_Hillbilly