I would choose a fairytale or fable for the short story and discuss the way it was enjoyable because of its simplicity, whimsy, and moral that should clear through the story without excessive twists or turns. Essentially, discuss the benefits of a simple and straightforward plot. As for the long work, choose a novel or novella that discusses a large topic within a complex storyline. For this I would recommend a book such as 1984, Fahrenheit 451, The Barcode Rebellion, or The Outsiders. All of these are great books that discuss various subjects of importance while creating a complex and enjoyable plot for the reader to follow. Shorter fiction tends to be a bit more lighthearted or whimsical than longer fictions like the books I recommended. (This is based in my opinion of longer versus shorter fiction, and there are outliers to my generalization, of course)