W231/HP38 would be a good powder to cross over into .40 S&W, as well.
But, I think Unique is a better "beginner" powder. It's very pressure-tolerant in 9mm (even if it runs dirty in low pressure loads), it has a fairly broad charge range, and it is not primer sensitive. (accidentally using the wrong primer won't cause significant pressure changes)
"Such is the strange way that man works -- first he virtually destroys a species and then does everything in his power to restore it."