There are so many smart, well qualified people who want to get into flight, that programs can generally be quite selective. I don't know exactly how you "blew" your last interview, but it sounds like you may not have realized some of the very real non-medical aspects of this job- that flight crews are a marketing tool too.
In addition to the actual CCT work, every flight program I know uses its crew in a PR capacity for the hospital-be it for safety fairs, fly overs for community events, or show and tell for nursing students.
Later, when you're transporting patients, every time you march into an outside facility/fly to a scene you are likely to be interacting with non-hospital affiliated staff. Those people will see you as the embodiment of whatever program's logo is on your flight suit and you have to make a good impression. Every program needs people who will market them well because this is a business like any other.
As far as I know, this is the purpose of the 5 minute presentation-to evaluate your personality, communication skills, and demeanor. It doesn't matter if you talk about puppies, scuba diving, or how to make killer tacos; what the program wants to see is that you are confident without being cocky, engaging, and articulate. Your topic should be whatever you can convey a personal interest in to the interviewers.
On a more long-term basis, if you're having difficulty with landing a job, you may want to consider ICU experience (I know, groan here). Depending on how much scene vs IFT work you do, programs may view that as better preparation, and it better compliments (rather than overlaps) with your medic background.