It is difficult to say which is better between IIT Mandi and top NITs, as it depends on individual preferences and priorities. In general, IITs are considered to be among the top engineering colleges in India and are known for their strong academic programs, research opportunities, and placement record. Both IIT Mandi and top NITs have their own strengths and weaknesses, but if you want to consider locational advantage, IIT Mandi clearly has an edge over NIT.
The program you are pursuing surely matters a lot but so does the college you will be studying at. College life is a major part of your life and the memories and experience stay with you forever.
In terms of academics and placements, both IIT Mandi and top NITs are good choices. You cannot doubt the quality of academics and placement scenarios at either institute. However, the campus life and peer group is what separates IIT Mandi from top NITs.
Ultimately, the decision should be based on your own personal preferences and goals.