IIIT Allahabad and IIIT Delhi both are reputed institutions, having friends in both the institutions, I might be able to share some of the things you may want to know before making a decision.

Listed below are some facts which will help to choose between these two colleges. 

• Ragging: All institutes come under a similar section, the reason being the law to prevent ragging is issued by the Supreme Court of India and thus, is applicable equally in all the institutes. There is no scenario of ragging in IIIT Allahabad and we expect a similar scenario in other institutes. 
• Placement & Packages: IIIT Allahabad has greater placement records than IIIT Delhi.
• Faculty: The faculty of IIIT Delhi is superior to IIIT Allahabad.
• Campus & Infrastructure: IIIT Delhi and IIIT Allahabad have somewhat equally good infrastructure. 
• Education Quality: Both IIIT Delhi and IIIT Allahabad have the same education quality.
• Alumni Base: IIIT Allahabad has a greater alumni base than IIIT Delhi.
• Coding Culture: The coding environment of IIIT Allahabad is far better than IIIT Delhi.
• Research Work: IIIT Delhi leads in research work.

The table shows a brief overview of the institutions:

Overall, IIIT Allahabad is a potential choice and IIIT Delhi as the second choice. If you opt for CSE or IT, do not think twice and go for IIIT Allahabad.