AA is the best in my opinion. Something you should know about AAdvantage accrual:
only B/H/Y economy classes earn miles unless you have a Canadian
only B/H/K/Y economy classes earn miles unless you have a U.S. or Canadian
mailing address. NO
BA miles on transatlantics (incl. Central/South America)
discount Y earns 70% mileage.
discount Y earns 30% mileage.
In your situation I'd try to find a Canadian address and go for AA and sign up for the Platinum challenge, 20.000 discount Y (10K full Y) miles in three
months (starts when you call customer service and ask to be enrolled in the challenge) gets you AA PLT. With PLT you get 200% the miles plus you earn 4 x 500mi upgrades per 10K flown as an elite --> these can be changed into 10K bonus miles.
Lots of interesting unpublished info about AAdvantage can be found at http://www.fewmiles.com
I don't know much about other OW programmes, Finnair Plus is crap IMHO, terrible award levels etc, but earns 100% kilometres in most oneworld Y classes (execpt BA/DI).