Historical data vendors...who to use or not !!
BarChartsonDemand.com . Good data but only have one minute bars. Focus is on Futures data. Have been around for a long time.
QuantGo.Com. Allow you to rent access to years of institutional tick data for low monthly costs ($275/month) but you have to run a virtual computer (with your choice of operating system) on their cloud platform.
TickData.com. Good data but they are expensive, especially when you need more than a few symbols.
Kinetick.com. Retail quality...other vendors listed here are higher quality.