Dear,

Both the colleges are premier institutes .Both gives best placement opportunities. If you are doing your mtech just to get a job iitb is the best option . If you focus on becoming a researcher then iisc is the best place. In terms of brand value iisc is higher than any of the iit’s. Though all iit’s have nearly same college culture where you study and have have fun. But in iisc the atmosphere is totally different.

So ultimately it's your decision. Decide your own path. Do not be bogged down by societal and parental pressure.

Hope this helps!