Candidates usually opt those that help in compulsory subjects too .e.g int relations for cuurent affairs its mine optional .along with sociology and pak ind history that help in pak affair paper.whats your educational background?

TPUM is new but looks to me for candidates having engineer background.if you feel it easy you can opt

You can go through syllabus of fpsc.download syllabus of css from fpsc.com and see which subject is easy or not.its totally depends on you.this and that can advise to go for it.you should trust on your abilities