Well when I up there to visit (I am from Schaumburg and a saluki) I stay at the Marriott on Michigan.. it is nice and close to most of the fun
The swissotel is awesome and a classy place.... there are a number of nice places and as other have mentioned and it is just what do you want to do...
Chicago is a big place, I like to stay near the lake, but that is a preference.
Make sure you have all the good stuff: Pizza, Hot Dog, Italian Beef, Gyro... so much to eat... so little time.
Now I have to plan a trip home
Good luck and have a fun time