I am an M.Tech, therefore, I will talk about this course.
Placements are the main reason why students with a good rank end up choosing IIT B over IISc Bangalore for their M.Tech.
The reason why you would go for your Master's is because you want to work in the technical field. Those who complete an M.Tech are technically very efficient. Working in a non-technical field after your M.Tech is not a good choice. You could have done the same after your Bachelor's. An M.Tech degree in this scenario becomes useless.
IIT Bombay has a good placement record for M.Tech students. However, most job profiles are non-technical. If you wish to go for a non-technical job after your M.Tech, go for IIT B or the other IITs.
IISc Bangalore will groom you in such a way that you will become passionate about your field of study. Many IISc Bangalore students reject non-technical job offers. Most M.Tech students at IISc Bangalore try to get a research assistantship at foreign universities to groom themselves for a research career.
These jobs are provided with the help of your faculty advisor. Therefore, IISc Bangalore does not mention them in its profile.
Overall, after your M.Tech or any PG program, if getting a job with a good package is your topmost priority, go for IITs. IISc Bangalore is a better choice for future researchers.