I'd say AA, if you plan to also travel to the US for business or leisure at any point. American carriers are always better with their programs when it comes to upgrading on their own aircrafts and other perks.

But check it out in some detail before diving in. Someone above mentioned the challenge they do. Without knowing too much about it, I would have thought the challenge would have to be accomplished on AA metal, not just One World partners.

I was a heavy QF and BA flyer for years, and indeed their service are the best if you are flying premium classes. I'd still say AA miles program would be easier to attain status and miles, however.