May I suggest that you find out what topics your school teaches in these subjects.
e.g. you might be interested in Ancient Greek history and then find that your teacher intends on doing mainly Egypt.
Also have a look at some of the different text books to get a broader idea of what each course involves.
Agreed. If you're doing Anc, make sure (for Year 12) your historical period ties in with your 'personality' (ie prominent figure within the hist. period)
Also, my friends who do Modern say it's a
lot of work, but if you're interested, definitely consider it.
Ancient - Cities of Vesuvius (Pompeii and Herculaneum) - a fair bit of content, and you have to know every aspect of it. And it's huge, but interesting.
Um.. by the way, if you do Rome (I'm doing Fall of Roman Republic), there's an insane amount of politics & propaganda etc - generally a lot of 'players' in the story. So if you get confused by that, better watch out (because I have no doubt the same will be true if you do Persia or Egypt).
Aside from that - basically, a lot of content, so you really have to know your stuff. But if you have a good tacher, it can be an absolutely fascinating subject.