Yes NIT Trichy is better than IIT Mandi.
Being a new IIT, IIT Mandi still doesn’t have a good infrastructure. It also doesn’t have good industry recognition. NIT Trichy on the other hand is old and well-reputed in the corporate world.
I have friends from both NIT Trichy and IIT Mandi. Based on the conversations I had with them, I will say NIT Trichy is better than IIT Mandi, especially if you consider CSE. The only advantage that IIT Mandi has over NIT Trichy is the IIT tag. Also, the weather of Mandi is better than that of Trichy. Trichy is quite hot.
The placement records, especially for CS at NIT Trichy are far better than that of IIT Mandi. According to the placement highlights of 2020, the placement average for IIT Mandi and NIT Trichy is respectively 85% and 92%.
Also, in terms of campus life, Industry collaboration, etc. NIT Trichy is ahead of IIT Mandi.