I was in Chicago for a convention, and I had one day free. I wanted to go to the Aquarium and/or Field Museum, but I happened to be in Chicago during Lallapalooza. I was not attending Lallapalooza, and I didn't want to be near there. I went to the Museum of Science & Industry because it was in the opposite direction when travelling from my hotel.
I enjoyed the Museum of Science & Industry. Note that there were a bunch of things which have a cost which is in addition to museum admission. At the time, that included a Pompeii exhibit, movies, motion simulator, flight simulator, coal mine, UR transporter and U-505 sub tour. So if you are pricing it out, watch out for that. I liked the Lunch restaurant there. Also Stan's Donut Shop had a glutenless donut, which I appreciated.