The location was a bit tricky to find at first. You just have to look out for a small sign on the sidewalk.
The attendants were very nice and helpful. I booked for a premium sedan and got a Volvo V60. I would have preferred a Mercecdes or a Caddy but they did not have them when I was there.
I would rent from Sixt Chicago again. One downside is that there aren't as many Sixt locations as there are other rental car companies'. If you run into a problem with your car in the middle of your journey and have to get a replacement vehicle, you won't be able to do that as easily as you might be able to do with the other companies.