Hello aspirant

Books best for class xi are

First complete the ncert book . Complete syllabus of class xi.

Start solving R.D. Sharma , a standard book for class xi.

For clearing theoretical concepts as concepts should be crystal clear then only you can solve MCQs. So refer M.L.Khanna, A Dasgupta, ARIHANT series.

IA Marin , Burman , Pishkunov for CalculusHall & Knight for Algebra

For jee  level preparation you must refer Balaji publications objective Mathematics by J. P. Arya.

Undoubtedly, NCERT Textbooks are best book for concept clarification and basic preparation. For reference, you can solve Mathematics for Class 11 RS Aggarwal. RD Sharma is an wonderful book for Mathematics. For Competitive exams, S L Loney, Higher algebra by Hall and Knight.