W231 certainly works in the 9mm, and is a very economical powder. But I've always found it to be rather dirty in an autoloader, and pretty smokey if shooting indoors.
After a few years of using 231, I switched to Titegroup in both my 9mm and 40 S&W loads, and couldn't be happier. More accurate overall (as sampled across a half dozen pistols), and much cleaner burning. And on top of it all, I think the recoil cycle is a bit softer when loaded to the same velocity.
Now, if I could just figure out what to do with 16 lbs. of left-over W231...
Neo