We take I-74, I-57, I-24, I-75, Turnpike. Depending on day of week and time of day, we may drive through ATL & always around Macon. I-57 & I-24 can seem very long because of the lack of big cities, rush hours, and lack of traffic that bring cities bring (if you leave early in the morning and the kids sleep, it doesn't matter what there is to look at). However, that is an opportunity to make some good time on the road as there is less congestion, less wear and tear on the roads thus less road construction. In the Champaign to Nashville leg of the trip, this is also 30 miles shorter than the I-65 route.
We leave after school is out and stop in Smyrna, just south of Nashville (~ 6-7hrs). The next day we arrive by dinner time. We usually don't drive straight through on way down as we are not as lively (awake) as we would like to be when we arrive to take on WDW. On the way back, we may stop, but often drive straight through - depending how early we start off.
For those of you coming across I-74 through central IL, we tried going down I-155, I-55, state route 4 to I-64 to I-57. Less miles, but took longer that I-74 over to I-57 because of traffic around STL and the 2 lane route 4. Have you found a quicker route.
What I have found from our road trips is Mapquest, Google, Freetrips, Rand McNally and other websites/trip planners' quickest routes show the most direct route via interstates. However, knowing traffic around metropolitan areas and road construction as previously posted by someone should be considered they can drive longer durations.