I am planning to travel to Kanyakumari next month from Delhi. Which Airline do you suggest? Thanks for your help in advance.

Why don't you check out Jet Airways. They are very good. See if they fly to Kanyakumari. Also Kingfisher is worth a try, though both of them are on little expensive side compare to Air Deccan, GoAir and Spicejet.

Have a nice journey.