If you have much luggage, take a cab or ride-share. If not much luggage, the Orange Line from Midway to the Harold Washington Library/Van Buren St. stop will be close to your hotel. The Blue Line from O'Hare to the LaSalle St stop will let you off several blocks away and then you'll have about a 10 minute walk (or flag down a cab for that last short ride).
Also take your time of arrival at the airport into account. If you are arriving during the morning or evening rush period, traffic is stop-and-go, so the train is faster.