I'm assuming you're in year 12, so I'd start out with a basic degree (i.e. arts) where you can try both. It's hard to get an idea of what major is best for you from HS, you really need to try them first. However, keep in mind that both PR and journalism are extremely difficult to break into because there are very few purely entry level positions. So when you get to uni, your focus would need to be on finding some industry relevant work to give you options post graduation.