Vodafone is the best in terms of customer service. At least they care for the customer and give personalized attention. Even the store representative gave her personal contact number for assistance any time.
The next best customer care is of Airtel. However, their store layout is a bit confusing for a regular customer but their service quality is really good.
Airtel and Vodafone are the best. Reliance, Aircel and Docomo have the worst customer care. They do not have proper knowledge and try to give lame reasons. Once, I had to run for a month to the Docomo store to get my new CDMA connection activated. Finally, I had to complain on pgportal for this harassment and then my SIM was activated by the appellate authority.