I’m from Kolkata, India. In West Bengal area there are many service providers but I would strongly recommend Vodafone! Yes, it doesn’t provide that much strong signal everywhere, like where I stay the signal strength is not so good, but still I use Vodafone!
Why? Because If you own a dual sim card supported device Vodafone is a must have Sim card, because It helps a lot while you travell, for example, recently I travelled Jharkhand, There Idea was not giving that strong signal but Vodafone had full signal with Internet connectivity, I would say at least you should always own Vodafone if you travell!