There are three major requirements for a data provider.

1. A good quality provider MUST provide data that is properly managed, and for stock markets, this means that the data must be properly adjusted for corporate actions like stock splits, and other  capital adjustments.
2. A quality data provider also needs to deliver quality data in a timely manner, so that analysis can be done BEFORE the next trade day.
3. A quality data provider will also be able to provide technical support to customers when there are computer issues (at the user end) that disrupt incoming data.

I have been a very satisfied user of Neuronet Systems for more than a decade, subscribing to their data services for a wide variety of markets. Neuronet Systems meets all the above criteria, and in addition, provides a comprehensive selection of markets, at affordable pricing.