While these tours seem incredibly awesomely cool, I can't help but feel that some of them are redundant, and thus wastes of the city's money...
Anyways, the "Railway Structures of Industrial Chicago" tour seems good. I've always been a fan of our warehouses and factories.
The Santa Fe building tour also would be nice - for various reasons, I've always wanted to see more of that building than the lobby. Also the CTA Station tour, and the Green Roof tour, if they go to the top of City Hall, would be amazing for photos. Lastly, Downtown Deco sounds cool, if they go inside the buildings, but it's given year-round...
Do some of these tours get only small numbers of people? I'd feel quite awkward going on a tour by myself, although I would probably learn a lot more.