RE: Most accurate, Worst, Favorite out of the box Muzzleloader.
The most accurate muzzleloader out of the box would be my Thompson Center Black Diamond XR. I took it from the box, with open sights, and using their suggested load of 100 grains of Pyrodex RS and a 250 grain shockwave, shot such a tight group at 50 yards, I thought something had to be wrong. It is a boring rifle. A very close second would be my White Ultra Mag.
The worst out of the box Muzzleloader for mewas a CVATracker Carbine. I have yet to figure out what it truely likes. Also the trigger was garbage, I sent it back and finally on the third time back, they fixed it. Not that I do not have some good ideas, but I have not shot it enough to really learn all its quirks.
My favorite Muzzleloader is a Thompson Center Renegade in .54 caliber. Its fun to shoot, accurate, and by changing out barrels, the rifle can do anything.