Hello Aspirant! If you are interested in research, innovation, and higher studies, IIIT Delhi is definitely a better choice among the three. But if you are interested in placement, infrastructure, and college life, should prefer NSIT or DTU for an engineering degree. In IIIT Delhi, every company visiting the campus for placement allows CSE, CSAM, and ECE branches and almost 75% of them allow CSD, CSB, and CSSS. Although there is a downfall in placement percentage at DTU and NSIT due to the COVID pandemic, they are still in a better position than IIIT Delhi. DTU and NSIT are known for their great placement opportunities (NSIT slightly over DTU). Its not that placements are low at IIITD but less as compared to the other two (DTU and NSIT). So, at last if you're interested in research, and want a good depth knowledge in your subject then go for IIIT Delhi or else DTU is far better than any other college.
Hope this helps.