Powder Valley got in a bunch of Hodgdon powders and lasted at least through yesterday.
I'm doing OK for now in all my standard calibers, and have too much invested in what I have to switch to something else. If I were starting off I would definitely be looking for something in an available caliber such as .204, .243, .257, .260, 7mm. Not sure which AR15 calibers are available these days but 6.8 or 6.5 might be worth considering.
When I was stocking up aggressively (2007 and 2011) I focused first on a few calibers to ensure I had plenty of those: .40, .223, .30-06 Garand, .22LR in CCI/Blazer, and 12 ga buck and slugs. Only after that did I supplement with ammo and components for secondary calibers such as .30 Carbine, 9mm, .45ACP. I did very little additions if at all to .308, .38 and .44 mag (I no longer had a .44 anyway). Now that I once again have a .44 that is the only cartridge I ended up short on powder for, bullets are still easy to get for it.
My SIL came into the shooting sports just during the previous dry spell (2009) because he returned from overseas station. I gave him stuff to get by at first and then he stocked up like mad in 2010-2012 so he is good to go. Lesson learned: when it is available and reasonably priced, stock up for a years worth at least. Then you can coast through the next shortage. I am sure we will continue to have periodic shortage due to politics and economy swings.