Guess which airport in the is worst overall for departures? The one you most want to avoid, therefore, if you are out traveling this summer? The answer: O’Hare in Chicago. About 69 percent of the flights leaving O’Hare International Airport took off on time in May, putting the airport in last place in the country for on-time departures, according to government data. Perhaps no surprise because I believe it is the largest airport in the , but good info to bear in mind if you have control over your stopover flights.