every one has different opinions, it is based upon ones strengths, like for me in my BS hons. i studied isl history, pak affairs and UN human rights as minor subjects and had 4 gpa in pak affairs and UN human rights but 2 gpa in isl history, plus in matric my pak studies marks were more than isl marks so i opted indo pak history, and as i already said that no subject in low scored or high scored, as long as you prepare well and cover all the topics in syllabus,and i have seen some of toppers going for indo pak history, plus its the same history you been studying since school times and prepare you for pak affairs paper as well. :)
mostly now all papers are currents affairs based wether its isl or geography or pak affairs.
and if you are a beginner than i suggest that first read this it helps alot, http://www.cssforum.com.pk/beginners-guide.php
and read syllabus of optionals before confirming your optionals, if you choose your subjects on your own interests than it will motivate you as well more to study more and harder. :) good luck.