Take a look at the United program.

They have a lot of flights out of IAD, and they fly to Europe, Asia, and South America. Additionally, they have an extensive partner network which will take you almost anywhere in the world that you would ever want to go. You don't have to fly much at all (only 25,000 miles) to get Premier status and that will get you Economy Plus and a little more leg room . If you fly more, you will figure out how to keep yourself in first class.

If you have to travel to a lot of podunk towns, HHonors is probably the best program, because there is almost always a Hampton Inn in every town of any size in America. Hampton Inn stays are pretty predictable and count toward status just like a night at the Waldorf Astoria.

Good luck in your job!