All the books are good to prepare for BITSAT.

You can start your preparation through NCERT book to make your base strong and to clear your concepts and to build your fundamentals strong.

After that you can go through HC Verma and Arihant.

Mostly students prefer HC Verma book.

To score good marks in BITSAT you should also refer previous year papers to understand the exam pattern and level of the questions and mock test series for your practice.

Good luck!!