IACS Kolkata is counted among the top-rated institutes in India. However, if you are talking about undergraduate programs then joining IISER Kolkata will be better. IACS Kolkata just started their 5 year-long integrated BS-MS program. Whereas, IISER Kolkata has offered this course for over 10 years. The quality of teaching and infrastructure is definitely better at IISER Kolkata compared to IACS Kolkata.