Pros and cons with various choices.
Some of the cheaper off-airport lots leave a lot to be desired. A couple aren't much more than a converted gas station with a tiny lot -- and I expect that you have to leave your keys so they can move your car. You also have to deal with shuttle buses and that means walking to the shuttle stops behind the Hilton. That's a pretty good hike through the tunnels. I always wonder about those little lots when my flight wanders in at 2am. I'm not sure all of them are necessarily 24x7.
The ORD remote lots are a choice -- but remember that they are all outdoors and if you're at the far ends, you'll have the tram ride followed by a bus ride. The good news is that they are more convenient than the off-airport lots AND if you know what you're doing, you can completely avoid the I-190 mess at Mannheim.
The main lot is pricey ($26 a day). I use it for short trips. But the outside lot as well as the roof are the same price, so if you're parking in the main lot to get a covered spot, you might not necessarily get one -- you also might get pushed to the "wrong" side of the garage (T3 instead of T1) when it gets full, generally in the mid-afternoon.
I know people who swear by the hotel lots, even without an overnight stay. But the hotel shuttles often use the same shuttle area, so check where they will pick you up.