only two locations to stay, downtown, or close to O'Hare. If you go downtown, there is the Marriott on Michigan Avenue, not too pricey. O'Hare/Rosemont has many hotels, like Hyatt, Four Points Sheridan, westin etc..

Generally, the local clientele in Chicagoland is spread out.  Best bet is to spend part of your time in downtown Chicago (or River North, that section north of downtown and the east-west part of the Chicago river), and part of your time in the burbs.  I don't know about anyone else's experience with O'Hare hotels but I don't care for them and you might find better facilities NW of O'Hare (towards the Woodfield mall area, Schaumburg/Hoffman Estates/Rolling Meadows; or even north to Deerfield/Lincolnshire) or the western burbs (Oak Brook to Naperville).  It really depends on how your suburban bookings go.

While staying within the Chicago city limits, you shouldn't need a rental car (taxis, public transit, walking, and hired cars are much better ways to travel within the more popular areas of the city), but a definate must if you travel to the burbs.  Of course, if you decide to stay near O'Hare, you may not need a car at all.

Good luck,
 Bob

stick to the western suburban areas- any place in Naperville, Downers Grove or Oak Brook would be ideal.