Public Administration is obviously easier than Philosophy.
I have opted both for CSS 2021 so I can tell that you should only go for philosophy if you are good at understanding and remembering a philosopher's arguments/concepts, and can reproduce them in the paper in a coherent way.
Public administration is more about memorizing stuff, although it has some theories but they are way easier and nothing complicated like philosophy.
Go through the past papers of both and just read some content from any introductory book of these subjects. You'll get a good idea from it.