Which option is better between mechanical engineering at IET, Ahmedabad University and IT at DDU?

The decision depends upon your area of interest.

Talking about IET, it is one of the best colleges and mainly focuses on project-based learning and you will get projects for every subject. Also, the faculty is very experienced and highly qualified. Most of them are from foreign universities. In mechanical there are best faculties and labs.

DDU is a government Institute. IT field of DDU as I have heard is good and has good faculties.

If you love coding and algorithms you should opt for it, or if you love moving things and analyzing them you should opt for IET. Hope this helps you in making the decision.