While choosing between Kolkata or the Delhi campus students should apply to any one of them and not in both of them. Some commonly known facts regarding this are: -
People believe that it is easier to get into ISI Kolkata when compared to ISI Delhi because of the location and fewer competitors for the institute which is absolutely wrong. Both the institutes have the same cutoff and entrance exam. The criteria for the selection of students is also the same in both the institutes therefore it is equally hard for the students to get into both.
According to a report published it has been observed that students find it easier to get into ISI Kolkata when compared to ISI Delhi. The cutoff criteria change every year and for last year it was: -
Overall ISI Delhi is the better option here but ISI Kolkata is the safer one.