Any forecast beyond 2-3 days is little more than an educated guess. There are several computer models that forecasters use to predict the weather. Those computer models often have significant discrepancies beyond 24-48 hours because of the way each model processes information. The forecasts you see on TV or on the internet all depend on which model is favored by the people producing the forecasts. Each model has strengths and weaknesses, so over time they will tend to even out in terms of accuracy. So in answer to your question, neither forecast can be considered the "most accurate."
Here's the best way to plan for the weather on your trip:
1) Take a sample of 3 or 4 forecasts from legitimate sources other than the local tourism board (National Weather Service, AccuWeather, Weather Channel and a local TV station for example).
2) Use only the first 2-3 days of the forecast, ignoring anything beyond that. If I'm looking at the forecast on Friday, I would ignore any forecast beyond Monday.
3) For long-term planning, trust the CLIMATE as opposed to anybody's prediction.
4) Don't become obsessed with the forecast. You can't do anything about the weather except be prepared for it. If you allow the weather to ruin your vacation, that's your fault, not nature's (barring a serious life threatening situation like a tornado or hurricane).