Choosing the right optional subjects is crucial in the IAS Main exam. The interest of the candidate plays an important role here. First of all you need to evaluate your own interest; you should go for a subject if you are actually interested in that particular subject. If you like a subject, you can give a lot of time to study that subject without pressurizing yourself. Your interest will drag you to study more to know more about the subject. Thus you enjoy studying.
While choosing a subject as an optional subject in the IAS Main exam, consider your academic background also. If you studied the subject in your Graduation or in your Post Graduation then you can consider the subject as your optional subject for the Main exam. In this case, you do not have to put extra effort to learn the subject. You can just start preparing for the subject from the UPSC exam point of view. You would already have the base as well as a good understanding of the subject, so you can go through some recommended books for the particular subject for the IAS Main exam and practice answer writing. This way you will take less time for preparing for the subject. On the other hand if you do not have any background on a particular subject and you choose it as your optional subject, you will definitely have to develop understanding about the subject and then you can start preparing from the UPSC exam point of view. Thus, it is always suggested that you choose a subject in which you have a background already.
You should also take into account the availability of the study materials, coaching institutes, books etc. while choosing any subject. If you have available resources to study the subject it will make your learning process easy.
You should analyse the syllabus of the subject and the trend of the questions being asked in the UPSC Main exam. Then find out if you are comfortable enough to study that subject. You take your own decision in choosing your optional subjects. Do not consider anybody else’s likings and preferences in choosing your optional subjects. If you like the subject in every way you should go for it even if others consider the same subject as difficult or not good enough to choose for the Main exam.