Why not join both American & United programs? You will always be flying different airlines based on where you are traveling to/from and they belong to different partner programs. You will never be able to find one program to satisfy your needs. With the Star Alliance and One World Alliance partners all over the place, you can use majority of the airlines. PLUS, if you reach a higher status with one program, usually the other program will match your status as they want your business. Only drawback with Seattle is if you fly AS, you can get the miles for flying on AA program but you won't get the bonus miles for booking online. Small penalty to pay for worldwide resources in the future.