IMHO it depends on what you're looking for. Features: ease of use, cleaning, etc.. The Knight Disc is a great muzzle loader and the discs make for quick and easy shooting, they just tend to be messy to clean. The Thompsons are good rifles as well but as with other rifles similar to this I have seen sticky primers and they are more finicky with loads. Austin and Hallock are one of the most accurate but are IMO on the heavy side. My preference is the Knight Disc Elite. Tapered barrel, well balanced and deadly accurate with the U shaped lug. I have had mine for over 15 years and it shoots MOA to this day.
I purchased two Knight Disc Extremes for a friend and they both shot MOA on the first shooting session. This all said it is like others have said: Ford, Chevy, Dodge.. Buy what appeals to you, options, balance, fit etc..
Just my two cents..