Which college should I opt for, IIT Mandi (EE() or IIT Dhanbad ECE)? I am really interested in computer science and I have heard that branch change is comparatively easy in IIT Mandi.

IIT Mandi is a comparatively better option than IIT Dhanbad. IIT Mandi offers effective classes with good college facilities and an eco-friendly atmosphere away from the rush of the city. 

Most significantly, you can easily change the branch after fulfilling the required criteria. IIT Mandi provides good hostel facilities and a resourceful campus to the students, which will help them study in comfort. 

IIT Dhanbad will stress you with work and exams and is not good for your research work, but they offer commentable extracurricular activities to the students. If you are highly passionate about your studies and looking for a career in security, then you can definitely opt for IIT Mandi.