UPSC

Hi Vikas,
Choosing an optional is a difficult task. One can't choose an optional based on one's academic background.
It depends on the factors like -
Availability of the material
Availability of reliable faculty / mentor with a proven track record. For eg., M. K. Mohanty for Public Administration (Synergy), Upendra's for Sociology (runs his classes in South Delhi), etc.
One needs to also figure out their own way of understanding and interest in any particular subject.
Good luck.

Please be clear which UPSC exam. I am assuming you are talking about NDA if so the stream does not matter. only you have to be clear about general knowledge but Science stream is preferred.

UPSC is certain branch with limited number of attempt. So you should take it as second option.
So, do MBBS after that you can try for UPSC.
I hope it helps.

UPSC conducts CAPF (Central Armed Police Forces) AC Examination for the posts of Assistant Commandants. This written examination is to recruit the eligible candidates in Group A (Assistant Commandants) in CAPF consists of BSF, CRPF, CISF, ITBP and SSB. All candidates with graduation degree from a recognised university are eligible to apply for CAPF AC Examination. You are eligible for appearing in examination.

You can pursue BA or B.Com, it doesn't matter. For UPSC any recognized degree is valid from any university. Thus, any graduation stream is sufficient for appearing in competitive exams.

The best option would be to go for arts in order to prepare for UPSC because major arts subjects are included in the syllabus of UPSC. Also, if you pursue graduation then it will automatically help you to prepare for maximum syllabus of the UPSC exam which will help you in clearing the same.

All the subjects of arts, science and commerce field are included in UPSC. You can choose any subject of your choice.