I am using airtel from last 6 months . The pack of 399 is good and have money values. As we use it on android definetly it will will give 5-6 mbps speed but in other aplications like uc or chrome the speed get too low. And some time it get some network issues. But speed at which I am using had great experience although it is indias biggest telecom service it giving good experience to the customers.
The pack of 399 also realy good . If any ask me about which servise provider should he use I will suggest him to use airtel.