IIIT Allahabad is better. It has a better curriculum and an active coding culture. The CSE and IT syllabus of the institute are designed according to the current industry trends. You will learn through real-time case studies.
IIIT Allahabad placements are excellent. During the 2022 placement drive, the average CTC offered was INR 30.63 LPA. The highest international CTC offered was INR 1.21 CPA.
As I have friends in both the IIITs, they have learned that both are great in their own ways. However, there are some points to give you a gist.
On the other hand, IIITDM Kancheepuram offers 4 bachelor's degrees (Computer engineering, ECE, Mechanical, and Smart Manufacturing).
At last, you need to set your area of interest and your comfort zone to see which colleges fit you better. If you are looking for a happening college life, then go for IIIT Allahabad as the college life at IIITDM Kancheepuram is boring with the least exposure and least entertainment options.