The Australian is probably the best, with the Yugoslavian running a close second.
Australian ammo is packed really well. There's some on the market in the U.S. now that's highly desirable but very expensive.
AIM Surplus has it in stock, or did yesterday. You can see how well it would lend itself to long term storage. It's not reloadable, but then, of all the surplus ammo I've ever gotten, only the Greek made .303 British was Boxer Primed. Interestingly, we use an ignition system in the United States which was invented by a British Colonel (Boxer) and just about everybody else uses an ignition system invented by an American Colonel (Berdan). Still, the Australian stuff is sure fire, not dirty, and it's brass cased as opposed to the more common copper washed soft steel.
Some years back, a huge amount of Australian 7.62X51, stored in blister packs inside of cardboard boxes, was imported and I bought enough to fill two large ice chests. I haven't shot this stuff because it's so much better packed for long term storage. At the same time, I bought six ammo cans full of the same ammo in bandoliers, on stripper clips. I did shoot a lot of that and it was primo.
Right now, only the AR-15 fodder is around as far as I know, but if you keep your eyes open and swing by the web pages of AIM surplus, Southern Ohio Guns, Samco Global Arms, Century International Arms, Classic Arms, Centerfire Systems, CDNN, and the other players you never know what will pop up. Just have the credit card handy because when it does show, it gets sold out most riki tik.