Choosing IT at any of the mentioned colleges depends on what you want to make your career in. If you are good at coding then IIIT Allahabad will be a good choice. The course curriculum is designed to provide you knowledge of DSA, OOP, and so on. You will learn more about coding at IIIT Allahabad than at NIT Allahabad.
IIIT Allahabad also has a good student environment which will help you in acquiring knowledge and keeps you motivated.
If you are not passionate about learning to code, then NIT Allahabad will be a better choice. In NIT Allahabad, you will meet students from a diverse background that will help you improve and groom your personality. The institute will give you wider exposure. You can prepare for examinations like UPSC or CAT And can also start your own start-up. NIT Allahabad has a better brand value than IIIT Allahabad.
Therefore, you can choose either institute as both of them are equally good. But coding is important to get a good placement in MNCs. So choose according to it.