One of the best places for South Indian food that I have come across in Mumbai is Madras Cafe at King’s Circle in Matunga. It is a little far for us to go, but we go there once in a while with friends. There is invariably a queue so expect some waiting time at peak hours.
The taste is amazing, and the lightness of South Indian food can ensure that one could eat and eat and eat! Don’t get dissuaded by the simple setting – that’s part of the charm.