There's huge cry that Madurai idlis are best. Having stayed in Madurai for 7-years, I can give assurance that they're crap. Madurai foods (especially available in hotels) are of poor hygiene and poor in taste. But, I always like the people--they're friendly and helping.
My favorite is always Azad Hotel's (Nagercoil, near Tower Junction) chicken kothu parotta. Nagercoil food like aviyal, samba (red) rice, etc are always good and healthy as they're cooked in coconut oil and with high hygiene--even in hotels.