Is it a better choice for choosing FMS Delhi over IIM A or IIM B when compared to placement salary?

There is no question at all if you are optimising for salary in the short term. On average, you would earn more at IIM Ahmedabad and Bangalore than at FMS. In the long run, it will be much more dependent on you and a little bit on the profile you want to work in. However, ceteris paribus and on average IIM Ahmedabad or IIM Bangalore will earn more or as much as an FMS grad. Choose A or B if you want to maximise your placement salary.

Whether you should optimise for placement salary is a different question, and the answer depends on what you want to do with your life.