If you are going for elite status, be aware that CO flights do not count towards elite status on AS, nor do CO flights get elite bonus.

AS is a good all-encompassing programme for occasional travellers as it allows you to dump miles from many airlines into it. However, only a handful, NW, KL, LA and AA, count for elite status.

If you were going for status, I would say NW or if you have an address in Europe, KL.