Hey there

If you'll have to choose between these two top institutes of the country then certainly it'll be a tough situation as both are very good colleges. But I'll suggest you to join mnnit Allahabad as the placements, the teaching and environment is better in case of mnnit Allahabad.

Check about mnnit Allahabad

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.careers360.com/university/motilal-nehru-national-institute-of-technology-allahabad-prayagraj/amp&ved=2ahUKEwj3n_SJldPkAhUe8HMBHVKeDs8QFjAAegQIBBAD&usg=AOvVaw22i-gMhxbqGhOoB_bkFxG9&ampcf=1

Check about iiest shibpur

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.careers360.com/university/indian-institute-of-engineering-science-and-technology-shibpur/amp&ved=2ahUKEwit29igldPkAhVRg-YKHditDK8QFjAAegQIBRAD&usg=AOvVaw1-q2gVG1UPhdgSKsNPBN7M&ampcf=1

Good luck