Hi!
I will like to suggest you that you should pursue the subject you are interested in.
Both economics and sociology are equally important subjects from the perspective of upsc, they are part of gs syllabus.( English literature has as such no usefulness when thinking from the perspective of upsc cse.)
And you hv the option to choose either of them for optional. So you are in a favourable situation where you have the option to go with either of them, so follow the one like the more.

All the best choose the one best for you!