Which stream should I opt to become civil servant?

More than the stream, a multi-sided approach is vital. Do well in your respective subjects to the maximum and then improve your General Awareness and English. English is always a very good library language.Your soft skills are greatly important. So, the task is on all sides.

Choose of a stream which you find most comfortable to deal with and prepare, be it arts or humanities.

Try to choose the one what you are working with. this will help you a lot being a manager / engineer in future. you will avail your promotions on that bases, most probably.