Hey,
For pursuing UPSC CSE, there is no as such best degree. UPSC has itself emphasized that candidates who have pursued their bachelors degree in any field are eligible for the UPSC CSE Exam. Also, if you see the list of selected candidates, they belong from different backgrounds.
Even if you choose BA or similar courses, you will not get much help because you can only choose 3-4 elective subjects in BA, and UPSC has a lot more syllabus. However, you still need to cover a whole more aspects. The best thing to do is to pursue the degree in which you carry more interest. This is because you can choose that subject for your optional papers which acts like a deciding factor.
So, apart from searching for the best degree out their you need to discover your area of interest, then only that degree can prove best to you. Moreover, college exposure can help you a bit in gaining confidence but in overall, you need to prepare yourself for the UPSC Examination. Many distance education students also clear this exam without going for the top colleges as such.
You can know more about preparation tips for UPSC CSE over here: https://competition.careers360.com/articles/how-prepare-for-upsc-ias
Hope it helps.
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