Congratulations Naman Sir!
I'd strongly advise you let him pursue an MTech from IISE. In my opinion, a person who secured first rank has both the passion and the capacity to do great things in the discipline, so joining a PSU at this point will limit his capabilities.
If he does go for an MTech, he'll still have the option of joining PSUs later, but he'll also have the option to do great things in future.

Hello Naman ji,

Pass this decision to your son. What inspires him most will be most appropriate option to go with. If he is interested in further studies, then IISc will be best as it is the most well-equipped institute in India. He has all the option open to go with. 

Most important thing is Suggest him that choose as per his choice. Which work he will enjoy. 

For best possible option for him, Use following link-

https://engineering.careers360.com/gate-college-predictor

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