Route 20 is OK, once you get west of Elgin. Before that, you're stuck in traffic. The only really decent routes as alternates going west would be I-88 to rte 47 north to rte 20, or I-94 west, but I94 is under construction in areas and is slow.
Or, 7pm thru 5am on rte. 20, but watch out for deer!!!!
I wouldn't do that. The stretch between IN-49 and Il-47 is not really worth seeing IMO and will take you a month to travel it. It goes through some questionable areas, and a lot of it is 4 lane road anyway. Don't even think about taking US-30 IMO.
Do yourself a favor and go around. If you really want to see the skyline/downtown, do it via the slab, but stay very alert. I hate driving the cage there anymore, too many crazy drivers on the streets. The toll roads are a little better, but not by much.
I-80 through Joliet is a train-wreck with road construction right now. I've had good luck bailing off at I-355 north (toll) to I-88 (toll) west to bypass it all. IL-47 is about the western edge of the Chicago suburbs.