Hello

There is heaven and Earth difference between IIT's and NIT's. If you are interested to opt for mechanical domain you can apply in any of these franchisee. These are top most reputed institutions. For admission you need to score atleast clear the cut off of JEE main and then score a decent score in JEE Advanced.

Hope it helped you

Good luck

See this information is very unclear. Since Mechanical is one of the oldest branches, most of the older NITs and IITs should be good. Rankings of colleges dont account for branch wise ranking. For the top branches, pls check this article here