IIIT Guwahati is way better than IIIT Kalyani. Many of the students who were formerly enrolled in IIIT Kalyani. They left the college after analyzing the faculty, infrastructure, and hostel facilities.

My brother was in NIT Silchar before being a part of IIIT Guwahati. He went there and found out that many students were from IIIT Kalyani. Everyone has different reasons for leaving Kalyani. However, none of them were praising IIIT Kalyani.

On the other hand, they were pleased to join IIIT Guwahati. Some factors that make IIITG a better institute than IIIT Kalyani:

1. Faculty to student ratio is very good
2. Great infrastructure
3. Good hostel and sports facilities
4. Better academic syllabus as they follow their mentor institute IITG and IIITH
5. Location of the institute

Hence, you can definitely go for IIITG as an institute rather than joining IIIT Kalyani. As far as the branches are concerned, CSE and ECE are totally different. But, at the end of the day, you have to decide which college you want to join. If you give more preference to the branch, you should join IIIT Kalyani but if you feel like you can slide or change your branch after the first year, you can join IIITG.