I have been using Vodafone for the past 5 years, and have used it in Lucknow, and now in Mumbai. There is one thing that I would definitely say, that the connectivity of Vodafone is just superb. You can go in the remotest corners and yet network will be there. And this goes well both for the calling network and 3G that I use. The speed of 3G internet is just superb and I can access the heaviest of pages without any hitch. The only issue that I face is that Voda plans are a little pricey.
Even that is ok, but Mumbai rate cutter plans are minimal. I think Voda should bring in more calling plans. Rest, it is the best network