If your visiting friends who like airplanes, make the drive 1-1/2 hr to C77 just east of Rockford. 2 grass runways and a paved one. About 450 airplanes are based there literally from Jenny to jets. Depending on the day, you may want more than a day at the airport.
I have been into UGN. Signature used to be the bad guy, but even they have self serve fuel now that is "area reasonable". Call an see what they want to park, remember that their business model is jet services. I believe there is a club on the field that you may be able to tie down at.
GYY - I haven't been there, but other forums have said that is a good place and take the train into the city....