The old IIT's are considered to be the best IIT's in India. This are:

• IIT KHARAGPUR
• IIT BOMBAY
• IIT DELHI
• IIT MADRAS
• IIT GUWAHATI
• IIT ROORKE
• IIT KANPUR

NIT's and IIT's both are good in terms of academics and research. But IIT's are better because, it gives the student more exposure. The funding in IIT's for research is very high. Apart from this the placements are very good in IIT's compared to that of NIT's. So from an overall perspective its always better if you get a chance to choose then IIT's will be the best choice.

To know more about JEE ADVANCED visit the link below:

https://engineering.careers360.com/exams/jee-advanced

I hope this answer helps. All the very best for your future endeavors!