That is a pretty much impossible question to answer, especially without offending the folks who make them and are also on this forum. The thing is that each maker makes so many different types of barrels, grades, and variations, it is difficult to generalize. I personally prefer Rice and Getz because they are generally better finished and leave less work that I have to do. That doesn't mean that any other barrel will perform less well. Rice is the only manufacturer with reasonably modern equipment and they also burnish the bore and rifling with a carbide cutter when done. Given that, there might be some expectation that their barrels are consistently better, but they are still made one at a time by one person who can have a bad day or have a equipment problem. Of course the same applies to all the other makers who can have good days and bad days and variations in the performance of their equipment.
With a muzzleloader, the load (ball size, weight, and uniformity; patch weave, density, thickness; lubricant type, amount, and application; and powder make, granulation, and charge size) and loading and shooting technique as well as rifle construction can affect accuracy. The barrel is the most important part of the gun, but many other things can compromise its function.
As with most everything else with gun building, the answer to your question is "it depends." I really wouldn't worry about barrel quality or accuracy at this point. Just figure out want you would like to build and try to find a stylistically appropriate barrel. Unless you are willing to wait a year or more, the best barrel is most likely going to be the one you can get. Most likely, the barrel, whatever you choose, will shoot much better than you can.
