It's a tricky question to answer for several reasons. In longer barrels, the generalization holds true that the powder producing the most velocity in the shorter barrels will also produce the most velocity in longer barrels. The premise behind this is that the barrel is long enough that the bullet is still in the barrel after the peak pressure has passed. But the snubby barrels are so short that unless you can guarantee good ignition, the slower powders can still be trying to reach their peak when the bullet clears the muzzle. As a result, for good velocity consistency, you often need a faster powder. The other reason for a faster powder in snubbies is to hold down the nighttime blinding fireballs and the muzzle blast.
So, first, anything you can do to improve ignition consistency is a plus. The main factor in that is getting primers properly seated, which means pushing them in two to four thousandths past the point where the feet of the anvil are just touching the floor of the primer pocket, so you actually compress the tip of the anvil into the priming mix in the cup by that much. If you don't have a means of measuring this, just seat fairly hard.
The next thing is to choose a powder that will be mostly consumed in the short barrel. This can be difficult as primers often unseat the bullets before the powder burn gets well underway, another reason for choosing a relatively quick powder. It is also a reason for producing a very solid crimp. The
Redding Profile Crimp Die produces the best roll crimp I've seen. The
Lee Collet-Style Crimp Die is available in 357 Magnum (currently on sale for under $12 at Midway) and will also produce a stout crimp. Note that of the two, only the Redding die works with both 38 Special and 357 Magnum. The Lee die cannot be made for multiple case lengths and is not available in 38 Special.
Then you get to choose the powder. Personally, I would be using something like 231/HP-38 (same powder differently packaged) or Universal or even Unique to start. You can try Bullseye. One board member even went to Clays in his gun recently. You can play with slower powders, but will have fireball and blast penalties and will probably see the velocities become less regular.