However, this is simply a popular trend, and you don't have to follow it. It is best to make a decision based on your individual preferences.
First you should make up your mind regarding the domain you want to continue with.
Here are some information to make your decision easier:-
The main agenda of IISERs and NISER is to promote research culture and motivate the students to conduct extensive research as a part of their curriculum.
My friend was a student at NISER and she loved the research environment there. She claimed the physics faculties to be extremely proficient in their respective areas of research. In fact, the Head of the Department of Physics even bagged the Shanti Swaroop Bhatnagar Prize.
Specifically speaking, it has great scope in high energy physics and condensed matter physics. The lab facilities of the new campus are top-notch. Moreover, the UG course of the School of Physical Sciences at NISER is comprehensive and covers various areas of physics such as quantum mechanics, relativity, cosmology, etc. The best part is that you get the chance to attend 242 credit coursework in rider to fulfill your MSc integrated course.