Hello Harika

You should go with Nit Silchar because it has a better rating and ranking as compared to IIIT,Nit has a better infrastructure and facilities and is more older than IIIT so doing Civil from there will be better and even Civil Engineering has evergrowing industry buildings are always being constructed and that will never stop,the fees in NIT is INR 5.5 lakhs for 4 years and for IIIT it is INR 7.5 lakhs for 4 years, the average salary in NIT is INR 6.5 lakhs per annum for Civil and for IIIT it is INR 3 lakhsper annum  for ECE.

Hope this helps you