Whether you should opt for MnC at IIT Delhi or B.Math at ISI Bangalore depends on what you want from your graduation and your career prospects.

Academically both institutes are excellent and none is better than the other. So my answer entails the drastic difference in the curriculum and scope of the two programs.

Bachelor of Mathematics, ISI Bengaluru

This program has high-tech mathematical stuff and purely focuses on Mathematics. The Institute is smaller than IIT Delhi and ideal for those who have a single passion in life, Maths. The coursework consists of abstract algebra, analysis, probability theory, and so on. Additionally, it has compulsory courses in Statistics, Probability, and Physics as well. Although it offers some CS courses also, the program does not focus on Computer Science much.

Math and Computing (MnC), IIT Delhi

The curriculum of the MnC program is more inclined toward computer science than Mathematics. The program focuses more on applied mathematics, rather than pure mathematics. As a result, graduates from this course can start jobs earlier than those from ISI.

In a nutshell, if you are willing to go for higher education and research in mathematics, then ISI should be your goal. If you are a person interested in the practical application of concepts and want to eventually be employed in a company, then IIT Delhi is the best place for you.