Eshan
Dear student,
This is a subjective question based on what factors one considers while evaluating the two. If seen from academic point of view, IISc can produce scientist of world-class level. Many of them are found to be among the top scientists in the world.
If considered from the placement point of view, IITs are famous to recognize talent to work in top mulit-national companies at highest packages being offered around the globe and also to produce high quality entrepreneurs every year, changing the world through their innovative ideas.
And so it depends upon the scale you wish to compare them.
Hope it helps. Regards.