I have been using vodafone ever since it has acquired Hutch. before that I was using airtel and for some obvious reasons I am still using it. I have two Sim cards and both are of vodafone.
What has really pleases me in these many years is:
Great network coverage.
Vodafone Service/Customer Service experience is excellent.
Plans are great especially the STD ones.
Suggestions: 3G network still needs improvement.