4th for Saravanas, and Udipi Palace's dosai are better than Chennai's (although Chennai is my favorite of the three options listed, and is more consistent, especially in its entree vegetable dishes than Udipi).
Madras Mahal has the most delicate and spicy dosas, so if you like them, I recommend it. Sounds like the others, which I have yet to try, might have better non-dosa fare.
Of the three, I'd take chennai garden, However Sarvanas on 26th & Lex is becoming my favourite for non dosa vegetarian (Chennai garden still for dosas)