Which is the best option among mechanical at MNNIT Allahabad, CSE at PEC Chandigarh, and CSE at NIT Kurukshetra?

This totally depends on your choices and interests. As the college administration is unknown towards your logical mind in doing computer programming all day or managing a manufacturing unit.

If you choose Mechanical Engineering as a branch, it is far better than Computers, where the second one is more subjective than the first one. For this reason, you can easily become an expert in computer programming, and it is not so easy to become a mechanical engineering expert.

But if you are interested in mechanical, or want to appear in IES after completing the BTech degree, then studying mechanical from MNNIT will be the best decision for you.

Besides, if you want to take Computer Science to be settled in top MNCs, studying CSE in PEC will be the best decision for you, rather than studying it in NIT K.