Call it the Mile-High Miracle: Denver International Airport is the best airport in the U.S. in the first-ever Wall Street Journal U.S. Airport Rankings. Once a symbol of high cost and dysfunction, Denver soared in rankings of reliability, value and convenience.

The rankings scored the 20 largest U.S. air depots in 15 categories, from on-time reliability to longest walk. The rankings are designed to reflect what matters most to travelers, including categories like security-line wait times, Wi-Fi speed, average Yelp scores for...