You should definitely go with IIT Mandi. I don’t know why you guys always confuse when it comes to be in 2nd Generation IITs. You can look around how 2nd Gen IITs stands together with the Old IITs. If we talk about particularly in between IIT Mandi and MNIT Jaipur. You can once go through the NIRF ranking.
IIT Mandi is located in Mandi (H.P) which is a very good place to live your college life. In IITs you will get world class infrastructure, i don’t mean that NITs don’t have but in IITs you will get to meet people across all over India not like NITs in which most of the students is from their respective states.
And when we talk about the campus size IIT Mandi is spread over 520 Acres while MNIT Jaipur has only 317 Acres. Placements stats of IIT Mandi is so good. Let me give you my example. I am from Mechanical branch and i graduated this year i.e in June 2021. I have 3 offers and this happens not only with me. There are many students who has more than one or two job offers. So, I’m definitely sure about the placements stats of IIT Mandi is nowhere comparison to MNIT Jaipur. And the coding culture of IITs Mandi is so good. For more info you can refer this one Kriti Mehta’s answer to How is the coding culture at IIT Mandi, IIT Patna, or IIT (ISM) Dhanbad?
Another main reason to go with IIT Mandi is that the number of girls students is more here. Because for girls there is no fees i.e. free education. If you are a girl then its good and if you are a boy then its too good 😛