Relative accuracy of historical data compared to Forecast.IO, worldweatheronline

I am interested in a reliable source for average daily temperatures for yesterdays, and I'd  welcome any feedback about which source is considered the most accurate.

I had planned to implement a solution using a feed direct from NOAA until I spoke with a helpful meteorologist there who said that yesterday is considered 'real-time', and as the NOAA is a historical archive, I need to seek a commercial solution.

He did also suggest that wunderground etc would be using the NOAA station data, but pre-cleansed. Is that correct?

Thanks!