I want to prepare for ssc ,then what is better for me bcom or BA(political)?

Staff Selection Commission (SSC) is a competitive examination which has nothing to do with your academic qualification and subject matter. Further, the SSC is a screening test for shortlisting candidates for various All India Services posts besides those being offered through UPSC Civil Services examination.
SSC will require a good hand in all of these subjects - General Knowledge, Quantitative Aptitude, English, Computer Applications and Reasoning.
While B.Com may help you with an edge in Mathematics, BA Political Science, a small advantage in General Knowledge. Therefore, I would advise you to take that subject, whatever you are confident in. However, your goal should be to practice questions from all the subjects of SSC with precision and time-management skill.