I don't know about this particular competition, but in past Youth of the Year-type competitions I've been involved with, the best thing to do is to speak about what you know and are comfortable and passionate about. If the audience and more importantly adudicators can tell you actually put thought into composing your speech then thats the right way to go.
A lot of people talk about an issue in the public spotlight or media. The same goes with poverty/ world hunger/ AIDS, global warming, striving to be an individual/ conformity. These topics aren't necessarilly bad to do, they just tend to be overdone a bit.
There is really no right or wrong topic to do. It's more about what spin you put on it and your delivery that will make the difference.
