Civil Service require graduation in any stream from a recognised university of India. So, you can opt for any bachelors course from any university. Considering the pattern of the exam, it is more general studies based hence, any humanities subject like political science, sociology, geography etc is going to help you further in one way or other. You can take these subjects as an optional paper too as you will have an edge in these subjects. Besides the nature of the exam, if you are interested in sciences then you can go for bachelors in mathematics, physics, chemistry, zoology etc. and later on opt for optional.

Hope this helps. All the best.