Quote from Diode:
I've traded grains, currencies, bonds, Eurodollars, lumber, and of course the eminis, and I've never had a problem with QCharts' real-time feed for any CME or CBOT contracts. Their end-of-day data sucks, and they aren't always good about maintaining their historic data integrity, but in my experience you can trust the real-time feed.
Of course you'll get some bad ticks from any pit-traded contracts due to the human input factor, but they get corrected fairly quickly and you'll see both the original bad ticks and the corrected ticks on your charts.
Quote.com uses S&P Comstock as their data provider, so they are inherently only as accurate as S&P Comstock.