While I can't give specific pluses and minuses to the specific campuses since I haven't attended any of the schools I did grow up in IL and know a bit about each of the towns. Only u can decided which you will like the most, but my ranks would be:
1. Chicago
2. Urbana
3. Peoria
4. Rockford
Chicago you are in the city, have excellent transportation systems, great nightlife potential, and awesome food.
Urbana is a big sprawling campus, great university atmosphere, good nightlife and food.
Peoria while not exactly the best city is relatively close to Champaign and Chicago so you can go elsewhere for planned fun (ie. a weekend or day trip), and having several colleges/universities in town they get decent music and plays in.
Rockford is kind of the middle of nowhere. It's a good two hour drive to Chicago or up into Wisconsin, and definitely suburban (meaning that there won't be a whole lot to do during non-study times), but if you're more of a homebody or just looking for poolhalls and bowling type entertainment you'd be totally happy there.
Good luck!