I agree with hala_madrid. The Oral is highly subjective. My friend chose this year to talk about the issue of opening a mosque close to Ground Zero. My teacher advised against it because its not an issue that is in the Australian media, or affects us directly, yet my friend did it, and she got a 17 out of 20, at which my teacher said 'she was lucky to get that much, considering she did a topic I advised against.' Meaning my friends' choice of topic made a large impact on the marks she got. And someone else in a different class did the same topic and got full marks. Clearly her choice of topic made no impact on how the teacher marked it.
Also, I did the topic of selling uranium to India, and my teacher only rewarded it a 17 because it was too complex for my audience. She called it a thesis rather than a speech, which was true LMAO My point is, think about your audience- being a group of teenagers. Dont let your speech to be too formal, and too complex. Obviously a bit of formality is needed, but choose your words wisely so that it isnt too informal, yet to formal.
Yeah, that didnt give any help on what topic to choose LOL, but I hope it helps anyway