Taxis are available at the baggage claim (lowest) level. Ubers and Lyfts pick you up at the check-in (street) level. The Kennedy Expressway is under construction and traffic is always a nightmare. The Blue Line train to Clark/Lake is the fastest, least expensive option. When you get off the train, you can get an Uber or Taxi for a short trip to the hotel.
Because of the Chicago Marathon, getting out of the city and to the airport is expected to take longer than usual. It may not be easy to get a taxi or ride-share on the fly. We highly recommend talking to your hotel's concierge ahead of time if you want to book a private car service. You can also take The Blue Line train at Clark/Lake straight to O'Hare, which is the fastest, least expensive option. But you'll still need to get there by taxi or Uber which could be difficult Sunday morning with the marathon crowds.
The city totally comes alive on Marathon Weekend. You'll see thousands of people from around the world and their families to cheer them on. The line around the Nike Store will be epic. It's a very civilized energy. Some streets may have detours on Sunday morning, but you won't be locked in.