Sorry I am not experienced in a sense that I have not appeared in CSS exams yet but I have been following this forum for almost one and half years. I have gone through almost all threads of this group as I was also confused to choose between business administration and public administration.
However, according to my humble opinion Governance and public policies & town planning and urban management are entirely new subjects and are introduced by FPSC for the very first time. So, no one knows about their marks trend. However, Public administration is more marks yielding than business administration. And also business administration is very difficult for non business students who does not have prior knowledge of the subjects in Business administration specially numericals in financial management.

Seniors always suggest to choose public administration and tells that its easy than business administration and also has high scoring trend.

I Think seniors will agree with me