Well its up to you persosnally. But Modern History is not Australian History btw (unless your teacher decides to pick this obscure topic, which is relatively a rare situation). You don't just learn about WWI or WWII- theres China, Russia, Ireland, the USA, Germany, Japan etc for National Studies and Personality Studies that cover a wide range of historical figures. For your International Studies, you (or the teacher) get to choose from the Cold War, Arab-Israeli Conflict, Indochina etc etc; not just Conflict in Europe or Pacific.
But likewise goes with Ancient- ranging from Sparta to Rome to Egypt to Agrippina to the Persian Wars. Theres a wide range of topics that you get to choose from, or the rather, your teacher.
Do some research, and pick one that you'll find more interesting. If in doubt, ask your teacher and if you're unsatisfied with it at first during ur first term, drop it