Firstly, lets clear a very old misconception. Having a BA degree don't help you to get a UPSC job instead its all about your preparation. If you see the past year statistics then you will find that there are toppers of UPSC who are from engineering background or medical background. So in order to crack UPSC you should have the courage to prepare well as well as you should be very keen about your interest. If your UG subject becomes burden for you then the habit of learning gets hampered and as a result, a student can't prepare well.

So you should take BA if you are interested in arts else its better to take a subject of your interest as UPSC didn't have any subject specification, all you need to have is a bachelors degree.

Now Bachelor of Arts is a 3 year Undergraduate degree program in Arts which in detailed studies the appreciation and the sense under the arts. For example, in english literature, they learn the Psychology of the writer, the portions of life which the author have portrayed and what does that mean etc. So Arts is all about interpretation. You give a red stroke on a white canvas and you can image it to be the redness of rose petals or the blood. And the way you should decide the meaning is a relative thing. But Arts try to figure out the beauty not only as a stimuli but also a thought process and the reason what it is the underlying thought process that makes the artist to portray a beauty be it a story or a drawing or a sculpture etc.

Above I have just provided the analysis of Arts and what role it play. If you want to know more about the academic regions of arts then follow the link below:

https://www.careers360.com/courses/b-a-bachelor-of-arts

I hope this answer helps. All the very best for your future endeavors!