Hello aspirant,

I hope you are safe and doing good.

You can do BA in any of these subjects : Sociology, Economics, Political Science, Geography, and Modern History. These are optional subjects available in UPSC, which can beneficial for preparation in UPSC and you can score very well in those subjects. Basically, the best BA subject should be chosen in such a way that it has a link or some syllabus common to the general studies papers.

I hope you find it useful.