In my experience the most accurate powders are:
#1 - black powder
#2 - Pyrodex
#3 - T-7
#4 - all the rest
But - sometimes the difference in accuracy is almost imperceptable. An 1/8" tighter group at 100 yards usually isn't that important, and if T-7 or one of the other substitutes shoots almost as good and cleans up with much less effort, it gets my vote. On the other hand I've had barrels that would do no better than 4" @ 50 yards with a substitute powder, and shoot one ragged hole with regular old Goex ffg. Only one way to know for sure - spend some $$$$ [:@]and try a few different ones.