See if you are interested in Theoretical Physics then CMI is the best option for you to enrich research standards and mathematical proficiency.

If you are not sure about that and you want to explore both the experimental as well as theoretical physics and then build your research perspective then it would be better to be in IISC. IISC is also good in theoretical physics and one of the premiere institute.

So this is my perspective of taking decision. It may differ but this is pruposeful.

Have a great day!