Well both the institute are one of the premier institute of this country but. It actually depends on the particular interest. IISc Bangalore is more orientated towards research field and IIT Bombay is a classic engineering college where students are mostly motivated towards bagging an awesome package and work abroad or India whatever. They do focus on the research areas and a lot of extracurricular activities are also involved in IIT Bombay including enterpreneurship, hackathons, robotics etc.