As far as RAS goes- the subject/degree with most topics related to RAS or any other administrative services would be that of ARTS as you can check from syllabus of both RPSC or UPSC. The topics included in syllabus are from Arts domain.
However, we would advise you to consider other factors as well:
- Subject you are good at: Go for stream/degree where your interest lie or which you are good at. Like if you are good in mathematics/Science you should take degree in that, because your probability of scoring good marks and in RPSC interviews or otherwise it will count. The probability of a good engineer getting selected in RAS is more than person who is from Arts but with very low marks.
- Apart from RPSC the scope and job opportunities associated with degree: RAS/civil services are competitive examinations with high competition and there cannot be any surety of selection. So there should always be a decent backup, which of course would depend upon the stream that you choose.
- The quality of institute – it not only depends on degree, it also depends highly on institute from where you are taking the degree. If the faculty that is teaching you the subject for first time is not good then it will take extra efforts from your end to excel in that subject.
- Intensity of your goal: If you are in 12th now, degree is going to take another 4 years and lot can change in those 4 years. If you do take arts now and start studying for RAS but after 2–3 years, aspire for something else then what? Need to make your mind strong enough first.