Hi dear
The basic difference is IITs are INDIAN INSTITUTE OF TECHNOLOGY &NITs are NATIONAL INSTITUTE OF TECHNOLOGY. ... admission in IITs based on JEE ADVANCED score while getting admission in NITs is based on JEE MAIN.IITs are superior than NITs in every aspect
Best of luck!!

Well, a lot!

Firstly, II draws it's major of funds from direct MHRD which is  a central gov. organization while NIT draws it's funds from state gov. college

Regarding peer group, this is the biggest advantage, peer group at IIT is the best. As, atleast you can expect a meritious student of any category to be there around you. While at NIT, even at top NIT, there are many SC and ST who have not even qualified for JEE advanced or score 150 marks in JEE mains.

Regarding Alumni, majorly alumni's of IIT are more loyal than alumni of NIT

College fest of IIT are quite better and more versatile than fest of NIT

Infrastructure is also a stand out point of IIT. Leaving very few NIT's like NIT Trichy, NIT warangal, IT Surat or NIT Jaipur, all other NIT's have pretty old and obselete infra.

Regarding future studies, IIT's have better recognition at Ivy colleges like MIT or Harward, then definitely they have better presentable oppertunities for research from foreign

Regarding placements, leaving very few students, majorly students at IIT get the same package of the students at NIT.. SO, this is an equal point for IIT and NIT.

At the end, the social recognition which IIT students gets, an NIT student can't even dream of that!

Thank You