A simple response would be to credit to flying blue, however, if you have spare time you can check out all of them, from china southern, aeroflot, korean, and so on...
Focus on two things how much mileage they give you for lower booking classes (some give zero), and miles needed for redemptions for an award ticket. Once you have an idea of which once passed the test, look at the fine print.
And most importantly, let us know please.
