Garrett's is certainly worth a try. I've been into the location at State & Jackson quite a few times. It's popular with both tourists and the office snack/treat crowd. There can be lines (10+ or so) but they ebb and flow. When a line builds up they work hard to knock it down in my experience.
I believe the location on N. Michigan is similar, though maybe a bit more touristy.
I like getting a small bag of the mixed. It's tasty and probably really bad for me.
I find Garrett's to be particularly good when gotten for other people. It seems to make outstanding nice to meet you / peace offering / social lubrication. Junk food without the guilt for the recipient (it's a gift.. they don't have a choice but to eat it).
You can get nice tins of the stuff if you want things a packaged a bit nicer.