One site that I find interesting is http://www.forecastadvisor.com/.
Here is what they say for forecasts in my area. Appears WU is doing pretty good.
Weather forecast accuracy for Fort Myers, Florida
Last Month
Weather Underground 83.33%
The Weather Channel 81.25%
NWS Digital Forecast 79.76%
Dark Sky (forecast.io) 79.76%
AccuWeather 78.87%
Foreca 75.60%
MeteoGroup 74.40%
Persistence 70.05%
World Weather Online 65.48%
Last Year
MeteoGroup 84.83%
Weather Underground 84.13%
The Weather Channel 83.96%
AccuWeather 81.62%
Foreca 79.32%
NWS Digital Forecast 76.77%
Dark Sky (forecast.io) 71.53%
World Weather Online 70.73%
Persistence 63.03%