Which health insurance plan is best in india. I need it for my father who has to undergo an operation shortly.?

My father has to undergo a varicose veins operation shortly and i am planning to buy a health insurance plan for the same(in india). Which is the best one that i should go for. Is there some time limit after the date of insurance before which i cannot avail any benefit if i go for surgeries? I have minimal knowledge regarding health insurance plans and how it works. Please share some information regarding this.