There's literally dozens of models that would rate as quality muzzle loaders in the modern and traditional hunting realm.
Does he want to hunt with round balls, saboted bullets, or possibly both?
There are also scores of different traditional & modern actions.
Modern inlines have faster, shallower rifling which aren't designed to shoot round balls well.
Traditional guns can have either slow, medium or fast twist rifling which determines which ammunition type it will shoot best.
Cost is always a factor and beauty is in the eye of the beholder.
It's often wood vs. plastic or laminate, modern vs. traditional, balls vs. conicals or sabots, #209 shotgun primers vs. #11 percussion caps, American made vs. imported, lifetime warranty vs. no warranty, stainless vs. nickel or blue steel, removable breech plug vs. non-removable breech plug, single vs. double triggers, shooting accuracy at 75 yards vs. 150 yards, black powder vs. substitute powders, enclosed weather proof designs vs. non-weatherproof designs, using a scope vs. using open sights or fiber optics, longer length barrels vs. shorter carbine barrels, heavy vs. lightweight, thumbhole stocks vs. whatever... the list seems endless.
1 in 20" to 1 in 32" twist is basically considered to be a fast twist for shooting sabots.
1 in 38" to 1 in 48" twist is basically considered to be a medium twist for shooting either round balls, conicals or saboted bullets.
1 in 59" to over 1 in 100" twist is basically considered to be a slow twist for shooting patched round balls.
Quite often, with the proper load development, inexpensive imported guns can come pretty close to holding there own accuracy wise with the more expensive domestic models, but not always as good as the most expensive custom, or semi-custom hand made rifles.
Reliability problems usually involve flintlock models more, and not the percussion guns nearly as much.
Start shopping around some muzzle loading catalog websites like Bass Pro, Cabela's or Dixie Gun Works, and view some of the different modern and traditional actions and the consumer feedback that's posted on those websites.
Also, visit as many manufacturer's websites as possible and view & analyze their products to see what personal preferences your friend has. Most products fulfill their intended purpose just fine. It's largely a matter of personal taste, cost and how any particular rifle fits the buyer.
Then you'll be able to develop more specific questions about a particular action style or model.
