I have always been a Madras Masala* man (despite not being South Indian), because 1) their food doesn't make me ill, 2) they have a nice space (despite their buffet being a weird side alcove), and 3) most importantly, they have doses. A dose is a South Indian dish that's basically the love child of a crepe and a burrito. And it's amazing. Get yourself down to Maynard Street and check it out.
In the interest of full disclosure, I rarely go to Indian restaurants in A2 because I'd rather go to my parents' house. My mom is a better cook than any Indian restaurant and she always will make my favorites.