Which is better, IIIT, Allahabad for ECE or NIT Durgapur for ECE if I have a general 12k rank in the JEE Mains?

Before deciding on any institute you should analyze it based on different parameters. Check if the college provides good facilities like hostels equipped with a good and stable internet connection, good food, satisfactory infrastructure, and the most important, a good campus placement drive. Both IIIT Allahabad and NIT Durgapur offer above-average facilities. Here is a brief outline of the institute.

If we look at the placement scenario closely, we can see that IIIT Allahabad has a better placement record and gets more companies. They also provide a higher package to their students. This does not make NIT Durgapur bad. Even NIT Durgapur provides good placements as well as opportunities for higher studies as well.

Both the colleges have a similar kind of course curriculum and nobody can force you to study.

It is not fair to compare the two universities because both of them are unique in themselves and have their charm. So, choose according to your convenience.