WASHINGTON — About 100 million people are members of frequent-flier airline programs. But how do you know whether you’re getting a good deal?

Consumer Reports studied hundreds of routes and millions of trips taken over the past two years. The research found the best and worst programs.

Southwest offers the most award tickets with the fewest restrictions. JetBlue offers the fewest award seats. But both airlines had the best marks for cabin service, comfort and satisfaction.

If you’re flying the route between Washington, D.C., and Chicago, one of the top 25 routes in the country, Consumer Reports says it’s only worth it to use frequent-flier points over cash if you’re taking Southwest or United.

The study was conducted with Department of Transportation data.