I can load more easily and more shots between cleanings in my muzzleloaders with Pyrodex's softer fouling. I clean the guns with hot water as soon as I get home, oiling with Hoppes afterward, and have no rust problems. Pyrodex RS does not bump up minie balls to grab the rifling in my repro enfield musket.
Black has a harder fouling, I need to wipe the bore with a damp patch about every 5 shots when using it in my roundball guns (our hot dry summers may be part of this). The slip fit of the soft lubed minies in the musket works well with blackpowder.
I'm slowly using up 12 year old Pyrodex and mid-1990' Goex and Elephant blackpowder from an estate. Still have a few pounds to go.