I was selected for M.Mgmt at IISc, Bangalore. Is it a good option?

Both institutes are premier institutes and offer excellent Ph.D. programs. Based on my sister's experience who did her internship at the Machine Intelligence unit in ISI Kolkata. The institute has world-renowned researchers in the field of machine learning who have INAE, IAS, and IEEE profiles. Here you will also find people doing top-quality research in computational biology and other fields. The research environment is friendly and the PhD students are quite approachable.

As for IISc, it is one of the leading research institutes in India. However, a PhD from IISc is very challenging and you need to invest a lot o time and effort in the same. Moreover, most of the professors in IISc are world-famous always busy will their personal research work, and have little time to guide the students. This lack of guidance will delay your Ph.D. 

Ultimately, it is up to you to decide which one to go for. Both institutes are top-notch and enjoy global recognition. It's best to contact the Ph.D. students of both institutes to get a better picture.