Hello Shubham, Without a doubt you should go to Jadavpur University. The placements record are brilliant and right on along with top colleges like IITs. The best part is about the fee structure, 4-year engineering course would cost you around 12,000-15,000 for the whole course while the fee structure of IITs is about 1,40,000 per year. The quality of education at Jadavpur is better than most of the NITs.

Both colleges are good if you are looking for a core branch of Engineering. But you should go for NIT Silchar because of the reputation it holds as an NIT. Moreover you can get more scope there as compared to Jadavpur University if you consider the placements altogether and few companies offer a little lesser packages in Jadavpur University as compared to the NITs. But the placements for both the colleges are very good for mechanical engineering. 

Hello Shubham Gupta, i suggest you to choose Jadavpur University rather than choosing NIT Silchar. You can think that NIT is a national level institute and Jadavpur University is a state level university but on academics basis, jadavJad University is better.