Hey Sunil 

It all depends on you .All three are amazing colleges but have a really different set of pros and cons. DTU and NSIT are more established and well known . On the other hand IIiT Delhi is a never establishment and has a little different environment as compare to NSIT/ DTU

IIIT Delhi is a research oriented college and is too good at academic so if you want to be true engineers then go for it. If you want a big brand name and a huge campus then NSIT or DTU is a better option . Speaking about the placement DTU and NSIT have highest packages offered but when it comes to the percentage placement IIIT delhi leads them

Hope this helps!