Many students go through this dilemma after clearing their JEE Advance whether to choose Computer Science in a new IIT or to choose any lower branch in the old IITs. Following information can help you in taking the decision better:
In short, I have discussed both the colleges (here IIT Kharagpur wins) and both the branches (here Computer Science wins). So, it solely depends upon the interests and priorities of the student whether to choose Chemical Engineering at IIT Kharagpur or CS at IIT Mandi. If you do not enjoy working with codes, then IIT Kharagpur will be the best option for you.