Any 100-115 gr. cast bullet, 2.5-3.2 gr. Bullseye. Someone will always argue about this next point, but use Small Rifle primers in .32-20, regardless of the propellant used. Many will insist this will cause mis-fires because a Small Rifle primer is too hard for a revolver, but this is simply not true based on 50+ years loading this cartridge.
You can also use a full case of Trail Boss, to the base of the bullet, not compressed.
.32-20 tends to squib in revolvers due to the long case. Using the Small Rifle primers, easily ignited propellants like Bullseye, or bulky powders that fill the case all serve to prevent squibs. You will see far more .32-20 revolvers with bulged barrels than any other caliber. This is because of their tendency to squib and another cartridge be fired behind the stuck bullet.