Choose a topic you're interested in, and that you want to learn more about. You'll be spending a fair amount of time researching, so picking something you want to learn about will make the process less painful.
Is there a topic related to your career that interests you?
Sometimes browsing the textbook from one of your classes can give you ideas on topics to write about.
Your instructor may provide you with a list of topics to choose from. Be sure you select a topic that fits within the requirements of the assignment.
Picking a topic that you already strongly support or oppose isn't necessarily a good idea. If you have a bias toward one side of the issue, you might overlook strong evidence that supports the other side. It doesn't matter what "side" you are on -- only that you have strong evidence to support the claims you make.