I'm flying to Rio in May on Continental and would love to know which program I should join to start earning miles on. Continental, Northwest or Delta? I'm a Mileage Plus Premier member so really only fly United now. Would actually like to start earning miles on Continental or Northwest because they have direct flights from LA to our hometowns. Also, do you think it's worth writing one of these airlines to try and get elite status? I love being Premier on United. Thanks for your input!