To be an IAS officer you need to pass graduate from any recognized university. So most of the aspirants prefer humanities degree courses over any other course due to the fact that it helps them a lot during the preparations. By the UPSC Syllabus B.A. is the most suitable option for IAS preparation because of 50 to 60 percent syllabus cover with B.A. Syllabus and also you may take an optional subject by your B.A. Stream as per your interest.