Congrats!!  Both are amazing colleges. You should go for NIT Allahabad .

NIT has better brand value than IIIT.

NIT Allahabad comes under top NITs in whole India

NIT Allahabad  has slightly better placement.

Better College Campus.

NIT Allahabad CSE(Best branch at this college) closing rank : 4700

IIIT Allahabad IT(Best branch at this college) closing rank : 5900

Thank You