Which course should I opt for in UG, BA, B.Sc or B.Tech?

If you are solely into IAS, it is better to opt for arts. It will be very helpful for you as most of the course of IAS is covered in its syllabus.

B.Sc is a better option.

Any graduate student can appear for civil services examination. Civil services is very competitive and probably toughest examination in India to crack. Therefore, you are advised to choose an option with standby career. B.Tech is definitely a better career option in comparison to BA and B.Sc.