One of my friends chose CSE at BIT Mesra over IT at IIIT Allahabad. However, he regretted his decision and after a month, got admission into IIIT Allahabad IT through the CSAB spot round.
BIT Mesra has a huge campus, however, its student intake is much higher as compared to IIIT Allahabad. Even in terms of location, Allahabad is a better choice than Mesra.
In terms of placements, the average package for BIT CSE stood at INR 19.27 LPA 2022. At IIIT Allahabad, the average package for B.Tech stood at INR 30.68 LPA during the same year.
The course fee is also much more affordable at IIIT Allahabad. The total course fee for B.Tech IT from IIIT Allahabad is INR 8,44,700, while at BIT, the B.Tech CSE course fee is INR 13,04,500 (does not include the hostel fees at both).
Thus, I would suggest you choose IT at IIIT Allahabad over CSE at BIT Mesra.