Vodafone has one of the best network coverage area. Very rarely have I been out of coverage area. The call, SMS and internet prices are also pretty reasonable.
The best part is their customer service, who will be available 24 X 7, and any query you make you get instant answer as well as action on the same.
I have been using from past 6 years and have good offers as well. One of the best features is their 3G internet, which has a good speed. Overall it gives a good customer experience.