It would be best if u choose the subject u studied. But in case u r not confident of the same, try to opt for other popular ones like History, Geo, Pub Ad etc. Firstly go through the syllabus of each, especially the paper 2 part. And try to find if u can relate to those terminologies. then refer to previous questions. Choose one, and stay put, no matter what others tell u on its demerits. Hope this helps.