I chose debt, but only because it is the biggest threat on a concrete level. The younger you are, on average, the longer you will live and the longer that debt will hang over your head and threaten to turn your life into economic misery.
But each of the choices you offered are negatives. We, who are already Objectivists understand Objectivism as framework from which to view those issues. While those who aren't Objectivists will just see the named negatives - which may or may not be clear in their minds.
I'd think that to attract new people to Objectivism it might be better to hold out some positive that promises to overcome some negative. Remember Harry Browne's book, "How I Found Freedom in an Unfree World"? Great title -one that prioritizes and encourages imagining a positive future against, and in spite of a negative background.
But you need something can seque into Objectivism very easily for the newbies. National debt levels can be examined and critiqued from an Objectivist perspective, but the individual can't change our economic system so it doesn't really take away any fears in that context.
And there should be something to attract the kind of people you want.... for example, you want people that are open to intellectual pursuits as opposed to those who would walk through fire to avoid a discussion of ideas. "How Thinking People can find Happiness in a Chaotic World"? And if you want a younger crowd maybe put in a sub-title like, "The Millenials Approach to Avoiding Life's Traps."
Or, "Integrated Life Principles as the Key to Inner Security: How millenials are learning to find happiness in work and romance." That one's kind of hokey and like a Tony Robbins come-on, but it would appeal to the demographics you mentioned.
Speaking of demographics, I have to ask, what's wrong with old white men, anyway? Are you getting all sexist, racist, and ageist? :-)