While both of these colleges offer good education, MNNIT Allahabad holds an edge over MNIT Jaipur. I have friends studying in both the colleges and their first-hand experiences clearly depict how better MNNIT Allahabad is.
Overall, it is highly recommended to choose MNNIT Allahabad over MNIT Jaipur any day. The better placement ratio, friendly and supportive faculty, etc, make it the perfect place for new engineering aspirants like you.