Here are some of my observations about different powders base on my usage.......
Pyrodex p--- Easiest to find, medium priced, most corrosive of the substitutes, works great, fouls less than real bp.
Real BP----- hardest to find, cheapest price, easiest to clean, easiest to ignite, the standard by which all others are measured. also the only powder that works 100% in flintlocks.
Black MZ----- somewhat difficult to find, expensive (twice the price of bp), can be difficult to ignite compared to others, cleanest burning of the subs, least corrosive of the subs.
Also the most difficult to meter.
Availability, price, application, and gun preference are the deciding factors in what I use.
P.S. Black MZ is a BP substitute made by Alliant powder co. it came out several years ago.
I should also not that many of the BP substitutes that are available are designed more for modern inlines, rather than traditional rifles...Pyrodex being the exception.