For those of you who travel between Chicago and Madison, let me extol the virtues of Van Galder. I usually take Megabus from downtown, and for the price it's well worth it to crowd onto a double decker coach and try to nap for a few hours. Depending on when I'm traveling, though, Van Galder's fixed price service is way more worth it.
First, service is from O'Hare, which means I'm already out of the city when we get going, rather than starting from the mess of downtown traffic. It's super easy to find the stop and there's an indoor waiting area instead of a curbside line and mobs of travelers pushing to get on the bus first.
The good news continues: so far, Van Galder has been on time or early for all my stops. I have yet to leave on time with Megabus, especially traveling from Madison to Chicago, when we are waiting on the bus to come from Minneapolis. Rides don't seem to be as crowded (that largely depends on travel time), and this leads to overall less hassles.
One thing both lines feature: friendly, knowledgeable drivers and staff. If you're gonna get one thing right as a bus service, people who get you safely from point A to point B would be it and in all my travels, my drivers have been cheerful and fully competent.