Question

which books should I prefer for ntse?

Answer 1

Very few and easy steps will ensure you get the NTS.

Stay true to NCERT. Especially for SST, read the class 9-10 books thoroughly. Like. COMPLETELY thoroughly. You'll surely get full marks in SST by doing this much. And that's quite significant.
Practice MAT from the RD Sharma MAT book.

Daily maths practice from standard books like RS Agarwal and RD Sharma is enough.

For science, again, stay true to NCERT and then study MTG Foundation Series books of class 9–10 of PCB. That'll do loads of help, believe me.

A final touch can be MTG NTSE Explorer.

That'll do.