Hello,

If we talk about placements, future scope and current market situation NIT's mechanical engineering will be the first choice. As there are many government job opportunities in Mechanical Engineering as compared to aerospace engineering.

But since you have interest in aerospace, it is also a good feild but the current market situation and iiest shibpur placements record in not that good. As if you do not get placed in a core company you have no chance to work on your interest. If you want to M.Tech, MS & research in this feild then only it is recommended to get in this feild. 

I would recommend you to go with Mechanical in NIT.