My advice is similar to others above, with some differences.

1. Join all programs. Join even the small ones like Midwest (formerly Midwest Express), though you can join those just before your flight with them.

2. If you are travelling 2 weeks per month, let the schedule and, according to company guidelines or customs, price. Do not let getting miles rule your life.

3. As you become more knowledgable about which airline suits you best, then you can choose them if 2 airlines have similar price and schedules. Flying more on one of those suitable airlines will allow you more upgrades as you rise in elite status.

4. If you fly certain airlines rarely, consider depositing those miles in Alaska Airlines. American, Northwest, Continental, and others (Hawaiian? British Airways? Lan Chile?) flights get Alaska credit. Of course, many airlines miles credited to Alaska won't get you elite status.

5. Don't sell US Airways short. They are not a bad airline. They fly between quite a few cities on the East Coast and a number of Southern cities. They also fly to the West Coast from their hubs.