Actually the Copper Point restaurant at the GRT serves some of the best south indian food I've ever tasted. And I live in MAA, I've eaten at the saravana bhavans, komala vilas (that's the same chain that runs the komalas restaurant in SFO), various other popular independent local restaurants etc. If you want chain restaurant south indian vegetarian food in MAA, there's this outfit called Sangeetha with four or five branches (Adyar, Anna Nagar, Mylapore etc) that's streets ahead in terms of quality, taste etc.