Fascinating. I think I’d say the Bean. It’s iconic, it’s visible, and unlike the Willis Tower, the area feels like downtown.
It’s remarkable how quickly the Bean has become iconic*, which I would attribute to its genius as a piece of public art. It’s fun to observe people around the sculpture – it leads people into the singular point underneath and around to observe the reflection of the skyline, literally pulling the reflected city into a single object. Which is to say the aesthetic concept of the Bean is to, on some level, be a Schelling point.
* Especially considering that it’s surrounded by other notable works that are bigger and/or have a more famous pedigree, such as the Gehry bandshell and Crown Fountain. Again, I think that says a lot about its success as a piece of public art.