William layton,
The type of powder used is dictated by the type of load (light target, mid-range, plinking, heavy magnum or hunting, defense, etc).
Generally, the target load requirements are met by fast burning flake powders such as WW231, Bullseye, the mid-range by Unique and WW231, and the magnum by WW296, H227, 2400, and H110.
As a rule, spherical ball powders (WW296, H110, etc) measure much more uniformly than flake, extruded, or flattened ball powders (Hercules, Red Dot, Green Dot, H227, 2400, WW231, etc).
HTH
John