Originally Posted by miles_kay
...Also once in a while BA has promotions with Diners Club and Starwood where you can get a huge bonus when you transfer... Sometimes double. They seem to be more consistent with these promotions than most others.
It's been a 50 percent bonus the past few summers - not something to sneeze at, but down from the earlier doubling.
Even within an alliance, each airline tends to treat its own elite flyers better than its partners'. For example, as top-tier (now mid-tier, but hopefully that exile ends in a few months) AA elite I never got a thing from BA beyond mandatory specifics such as club access and premium check-in. You may be QF super-titanium diamond, but as far as BA cares you're pond scum along with the rest of the unwashed masses (which includes myself).
If you might fly AA from the UK to the States, AA flights don't earn BA miles because of market share/antitrust issues, but they do earn QF miles.
Finally, there are differences in how the two programs reward different fare levels. Look at both carefully in terms of your purchase patterns.