It depends on what type of speaker you are. There's two main options you can go for:
1. Pick something that your passionate about, and have a firm position on. If you stick with your viewpoint and make a convincing argument, you should do well. This is the easiest way to score well.
3. Pick a topic that is not overtly political, economical, ethical or moral in its content. It could be the advocation of something mundane, such as the usefulness of pockets for example. Be creative if your going to go with this, but be able to justify your choice. This option is harder, but could easily make the better speech if done with flair and orginality.