Is IISc is better than IIT?

IITs are for those who are on the lookout for jobs and have little or no interest in research work. IISc on the other hand primarily focuses on research work. 

Basically, to pursue a career in any branch of engineering, the industry-oriented Bachelor's program offered at IITs is perfect. But for a research enthusiast who is keen to pursue a career in research, IISc is the best option.

Ultimately, the better institute is one that aligns with your preferences and area of interest.

For better reference, I have compared the IISc placement statistics with the topmost IIT Bombay

You can clearly see that IIT Bombay offers much better job opportunities than IISc.