I don't think people here realize the importance of having reliable data from direct source. It's like risk management when trading you make sure that you don't lose more than 1% on any trade and when it comes to data you search and download the easiest of them.
The thing to keep in mind is, and this a part of risk management too, getting reliable data (clean and accurate) which you can get from the real source - NSE/BSE because as long as there is NSE there is trading unlike other sites which may go down or discontinue leaving you high and dry begging for help. Secondly making sure that you data is compatible with the format NSE is providing because other sites may change the format, skip/rename fields, change filetypes or ask for a subscription you will effect your data feed/timing/analysis and other adverse effects.