I am totally biased as hinted by my username! I love the interdisciplinary nature of the program. I originally planned to apply to both programs but decided on HDFS for all 7 applications. At the end of the day, my decision was based on my desire to do mostly outreach work instead of building a career in academia which by the way I am not entirely opposed to. The HDFS programs I applied to were a perfect fit, I mean PERFECT. Depending on your options, you may have ample opportunities to engage in either/both path(s). If that is the case, it helps to focus on who your POI is, what he or she is interested in and what is the fit with the career goals. Also, look for best funding offers and research centers within the department and throughout the university.
Still, if you have always dreamed of being called a "psychologist" then the decision is made....mostly.