I have voted for muzzleloader.
I have my guns for fun, and the muzzleloaders are the most fun. They are neither fast nor easy to load, but pouring down 120 grains of powder and stuffing a .62 caliber patched ball down the bore is just something completely different than a semi-auto doing everything for you. With the ML system you need brains, with the modern systems just throw in the magazine and empty it. With the muzzleloader your shot is much more valuable because each shot takes some time to load. And it also feels more valuable.
And yes, I have 5 bolt action rifles, 1 break action shotgun, a semi-auto pistol and a revolver. The muzzleloaders are just too much fun. You have to be close and personal with each shot, you touch the projectile, pour down the powder, stuff it all into place, you get dirty fingers and smell the burnt powder.....