Choosing a Frequent Flyer program is sometimes more art than science—so many factors enter the equation (home airports, usual destinations, desired amenities, emotional connection, etc.).
Gabriel Leigh, author of the excellent Altimtr (add it to your source of air travel news!), dives into the topic and ranks the 10 best worldwide. Primer? American Airlines AAdvantage wins the top spot.
My opinion differs a bit, but it is well argued.