Even after covering a larger part of political science syllabus I switched to international relations.
Reasons for opting
1) repeated questions
2) definite syllabus
Reasons for leaving
the one and only factor: TIME. It takes too much time, especially in css, political science is not easy and mark giving as in bachelorsg and masters of punjab ,peshawar, etc university annual exams. One has to write qualitatively. And writing political thought and political systems in a qualitative way is indeed a herculean task. It is highly expensive in terms of time course graph.
There are other factors also. For instance it is boring and exhaustive as one has to memorize the redundant sources of political thought and the cumbersome political systems. Nevertheless, that may vary from person to person, as some people find it extraordinarily interesting .
Reasons for opting international relations .
1) the subject has more marking potential in new syllabus that is of 200 marks. Earlier, the paper gave less marks only in the years when the paper setter would design the question in a combined method. By combined I mean mixing theories or definitions with current affairs aspect of that theory. For instance , in 2012 paper, the same methodology has applied. As a result the question would turn out to be extra large and the candidates would miserably failed to answer the question completely . However, in new syllabus, the theory and current affair part has been clearly divided into paper a and paper b respectively. this division makes international relations interestingly high scoring. Especially it's first part is a definite syllabus like political science but not lengthy like political science. So it's short and solid, which makes it easy and scoring.
2) syllabus overlaps current affairs , especially part 2.
3) very short syllabus with proper guidance.
4) interesting. It's memory and repetition of course for preparation value is great.

AoA,

What are your rest optional subjects ? Have you opted international law with I.R ? If not, then kindly tell why ? You said that it has very short syllabus with proper guidance so could you tell which kind of guidance is needed in its preparation ?

I have to choose b/w political science and I.R. but at this point of time I am sort of confused.

Regards.

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Nasru minal'lahi wa fat'hun qareeb

Yeah , in my view IR is better option, particularly those opting for IL would overlape each other. More importantly in ce2014 IR was very scoring subject.

yes but its very broad subject, you almost cover all countries historical background in proper way; for example there may be question like
what is the strategic importance of crimea peninsula? how it leads to Ukraine crises and how it affects Russia as leading gas producer?
these are very cumbersome questions, you must have depth study.

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move fast and break things