Make an inventory, either mentally or on paper, of the topics that interest you most. Your interest in them will make researching them enjoyable. Plus, when you speak, it will be obvious that you like your topic and you'll convey your points with energy and charisma (see Reference 1). Aside from your own interests, the audience should also be able to relate to your topic. Choose a topic that will appeal to the emotional side of your audience as well as to your own emotional side (see Reference 3).
Try to choose a topic that you already have some knowledge about, even if you're only slightly familiar with it. You'll be able to use this knowledge to direct your further research. Also, you can branch your speech outline out from the knowledge you already have, simply adding to it instead of starting from scratch (see Reference 1). Your audience will be more likely to get onboard with your view on the subject at hand if you provide rational truths, facts and examples that can be backed up by proof (see Reference 3).
Topics that deal with controversial issues will not only be interesting to your audience, but they'll also be easy to research since a ton of information about them already exists. For example, topics that have to do with abortion and women's rights, race or gender, disabilities, gun control, health care and religion tend to spark controversy and will be good topics to speak about. If you're going head-to-head with another classmate, these topics also make for excellent debates (see Reference 1).
To test out how well you can truly persuade people depending only on your solid speech, choose a side of a topic that is wrong in terms of common knowledge but that you want to argue for. For example, convince your class that spoiled milk is actually healthy for you, that diet pills are a positive health choice or that your favorite musician should be voted into the presidency (see Reference 2).