Well, you are not the only one who is thinking so. Many candidates with Engineering and Medical Sciences background, opt for Humanities subjects.
Look at this year's topper Shah Faesal (CSE 09 Rank 1), a doctor, had Public Administration and Urdu Literature as optional subjects.
Tanvi Sundriyal (CSE 09 Rank 6) , an Engineer, opted for Sociology & Public Administration. You will find many more such cases.
The subjects you have short listed are all popular subjects and produce good results. The best way to move further is to have a look at the subect's syllabus and past year's papers so that you can get a rough idea about the requirements.
From General Studies angle, Public Administration, Geography or Political Science can render some help.