AA does not have a true hub at LAX but does have a focus city. UA is more focused on west coast service than AA is (AA relies on Alaska as a partner a lot there), but its hub is at SFO not LAX, and so doesn't have a LOT more longhaul nonstops from LAX than AA does.

In OneWorld, you can only upgrade with miles on the airline you're a member of. That means AA in this case. Which means no problem to Europe (you can simply upgrade LAX-LHR on AA and then do the short hop in economy on BA or another partner the rest of the way, plus have all-AA one-connection flights to cities like Paris, Frankfurt, Belgium, Zurich, Rome, Dublin, Madrid, and a couple others. But in Asia, SO FAR AA only flies its own metal to Japan (Tokyo direct from LAX plus other cities, Osaka through DFW), Shanghai (also through DFW), and Delhi (through ORD). Tho keep in mind that other than Tokyo they didn't have any of those a year or two ago.

*A theoretically lets you upgrade on alliance partners, but if I understand the upgrade charts correctly, it takes almost as many miles as an outright award would! And from what I've heard so far it's much more theory than practice (tho it's a fairly new program so it may get better, who knows). But UA does fly its own metal to Sydney.

Also, upgrades work differently at AA vs UA: UA, like so many airlines, only lets you upgrade internationally from "non-discounted" (or at most "lightly discounted") economy fares, so you have to pay more before you find out whether you can upgrade (unless you can see -- www.expertflyer.com -- that upgrades are available before you book). AA lets you upgrade from just about any fare you can book through them (an occasional deep sale fare booked through them, and many fares booked through consolidators, are not eligible), but you have to pay a $250 copay (if you're not top elite) each way (plus the miles). That works out to no more (and sometimes less) than the cheapest upgradeable fare at most other airlines IF you book in advance, but if you book close to departure and thus get a much higher fare you STILL usually have to pay the $250 copay. But the "nice" thing about this is that you're only charged the $250 if the upgrade goes through, as opposed to most other airlines where you have to pay a much higher fare whether the upgrade will go through or not.