I travel over a 100,000 miles a year so I have lots of miles and lots of experience with the airlines’ frequent flier mile programs. I’m usually pretty loyal to United because they have a hub near me and I have 100K status with them, but when it comes to using miles, I’m partial to Continental. They by far have the best web site, tools and programs to figure out when and how you can use your miles and to actually use them.
My favorite part about frequent flier mile tickets is that they are very flexible. You can (at least right now) change the day and time of your return at any time without penalty.
For keeping up on frequent flier mile program changes, I recommend The FrequentFlier Crier newsletter.