I used to have an airtel data card which is not too bad as long as you are doing very light surfing and the moment you try attaching something to an e-mail .. just keep on waiting for ages and any content rich page will take a long long time to load so I got rid of it and got a reliance netconnect card which is a lot better then the airtel gprs.

I have also used tata indicom's plug to surf thing which is not that great.. Till date I have liked reliance net connect the most.
I would love to hear from others about what they are using