Normally one should select optionals, which one is familiar with, or has at least studied till the graduate level. If you are not comfortable with the subject, you should not select the subject as an optional. But the choice should not only be as per your interests but also be baed on the study material available. Even science and engineering students take up subjects like history, sociology, anthropology, grography, political science, psychology and public administration because there is a huge amount of study material available in these subjects. Also keep in mind that you may have been proficient in a subject, but lack of touch may make it tougher to crack technical subject where freshers may do better. The competition is among the people who have opted for the same subject. One should top in his/her subject to succeed in the examination. The Point is, if you are an electrical engineer with 2 years of experience go for a new subject like pub adm or sociology. Analyse the syllabus of previous years and the question papers, and analyse past trends. Get some feedback/advice from seniors and fellow students who are well versed in the subject. Remember no subject is bad. History is good if you can spend more than 4-5 hours everyday. Geography is a good option if you can spend at least 4 hrs every day. Pub Ad, more than 3 hours. Sociology, more than 2 hours and so on.... So, it all depends on how much time you can spend a day and your liking of the subject. You have a very good memory then a technical subject may help else a social subject would be better. Lastly look for overlap in subjects like, sociology and pubad; history and political science etc.