Well, I have been constantly using Airtel from last so many years. In fact, everybody in my house uses Airtel only. From this you can easily guess that we find its service really good.
Though I agree it is a bit costly and has slow internet speed but as far as network coverage is concerned I am really happy with it. Even you will not face any network issue in villages too.
For postpaid services I don’t have any idea because I always prefer prepaid services and with Airtel I am completely satisfied.