I think Vodafone have the best voice clarity in India. And the customer care representatives are really professionals. I didnt have to wait for more time for getting a representative or to solve my query.
Really good service. The only downside is the rates. For eg, Docomo provides 4Gb for 95 Rs while vodafone gives 1gb only.
But I am 1000 times willing to pay for their perfect service when I compare the Pathetic Docomo and all..
All the best