O’Hare and Midway both have excellent service to the city.
The airports are almost equidistant from the Magnificent Mile (about 30 minutes by taxi). A taxi will likely cost in the area of $35-50, depending on the number of travelers and baggage, and you can easily get a van or taxi from the kiosks outside the airports. Follow signs in the airports to the taxi stands.
For individuals that want to save money, the “L” runs directly to/from both airports, and is quite convenient to downtown Chicago. Fares each way run less than $5. (See the attached CTA map below).
Take the Orange Line and change to the Red Line at the Roosevelt stop. Stay on the Red Line to the Grand stop; when you exit the station, either NUBC hotel will be a 2 minute walk from the stop.
Take the Blue Line and change to the Red Line at the Jackson stop. Get off the Red Line at the Grand stop; when you exit the station, either NUBC hotel will be a 2 minute walk from the stop.