I don't know that I really love any of these. Maybe the Volunteer Park Observatory would be better. But that said, I feel that Boe the scarf dancer is the best choice of any of these.
It looks like the winner will get around 1/4 of the vote. That means roughly 75% of the voters will be disappointed. That further means that you should have a runoff vote featuring the top two or three. Go Nutty!
The Black Hole Sun sculpture is a great idea, but it would require complex legal approval. I like the Volunteer Park water tower suggestion that I believe was offered on the stranger's slog. Either way, no people. Please.
If the competition is close for first (which it looks like it will be), we should do multiple denominations/versions of the bill, one version for each of the top three(?) images. Hee hee, collect all three!
I agree with Dod and other commenters on the "no people" thing.