After trying out many data cards, finally I have settled with tata teleservices broadband wifi connection. Speed seems to be ok. Service and bill also is reasonable. Daily usage if the connection is prepaid is sent everyday by the company to our mail.
So we are able to know how much is our daily usage and plan accordingsly. Charges for different categories of GB also is very reasonable, even though reliance is also providing similar rates. But Tata Teleservices is a better company to deal with, than reliance. The customer care is also ok, compared to most of the other companies. So overall experience so far has been trouble free.