I'd recommend short stories or small novels. You don't want to be doing poems unless you're really proficient at drawing out complex ideas from short and cryptic sentences. Conversely, avoid choosing long, arduous novels that are ridiculously long for obvious reasons, no need to create more work for yourself. I'd also steer clear of movies and the like because it's often difficult to effectively explain the techniques contained. However, if you're confident by all means.
Personally, I chose the novel Never Let Me Go by Kazuo Ishiguro which revolved around unknowing clones who were deliberately engineered for forced organ donation. This ended up being pretty good for the HSC as the question related to emotional discovery which was essentially the entire premise of the book.
Of course we can help you, but ultimately you'll have to research some texts on your own; you're far likelier to do well with texts that you are actually interested in instead of something chosen simply because it's popular.