Vodafone is among the best mobile service providers in India. I have been using it for almost 10 months now and I have not yet experienced a no net work situation. The network coverage is exceptional.
The 3G service can be a probelm in some areas but where the 3G signal catches it is very fast.The pacls are expensive though when compared to reliance but the service way better.
The service cenfre people are supportive too. So you can opt for Vodafone easily.