I could use W231 for all my pistol loads. I prefer to use AA5. The one exception is .45 apc. I could use W231 or AA5 but have found WST works better in .45s. I have a hard time trying to stick to a single powder. One powder doesn't always give the best results you can get over a range of different calibers.
Powder Valley has been out of AA5 for a while now. They are my first choice for powder and primers. I guess I will have to see how AA2 works for 9 mm. It is a good thing there are many choices available to us for pistol powders. If one becomes unavailable for a while you can simply switch to another and work up a new load. You might also find something that works better than the powder you have been using too.