I always told students to stay away from issues such as gun control, capital punishment, and abortion. These are too volatile for any hope of success. Most adults have already made up their minds on the issues and will not be swayed by a new speech for or against. And, in all likelihood, if the adult judge's belief on the issue differs from the student's, the judge will be able to rationalize a reason to rank the student in the bottom part of the panel, even though the speech itself may be better written and better delivered than others in the round. Nobody ever said life is fair or human nature is open minded.
Audiences tend to listen best to that which they hear the least.
Therefore, it is incumbent on the prospective advocate to search for an issue that has not been belabored and belabored and belabored by others. That is hard to do, given that virtually every aspect of life has been legislated or regulated time and time again. If issues that are common and recurring must be chosen for an advocacy, then it becomes especially pressing to write the speech from a new, fresh perspective-if at all possible. Otherwise the advocate will end up repeating someone else's ideas of a possible policy solution to whatever the issue. That is not to say that a sixteen year old must always offer a new and untried policy option as a solution.