I would definitely drop the car off. You'd be paying $45/day for the parking and however much more the rental would cost you.

How much luggage do you have? train from ORD would be $2.25 each. If you don't have too much stuff, that's an option too.

The Drake is easily accessible to transportation. If you want specific directions to something, just ask, there's plenty here who know the CTA well. Cabs around the area won't be too bad either.