Hyy Nitish
Political science is the best option, as compared to Economims

And if you opt Political Science as optional subject also it will almost complete 50% of whole UPSC syllabus

Political science will cover your subjects like
>International Relations
>Internal security
>CONSTITUTION OF INDIA
> Governance
> Social issues

And if you want to opt for  Economics  you can do but with this you have to study other subjects and notes with details and thoroughly.

All the best for your preparation
For more information please ask in comments section