Hey,
Can anyone tell which forecast is better and more accurate?
Solacast Solar or forecast solar?
Which one do you use for Energy Panel?
Interested too but I think this is a question without an answer, similar as asking which weather service provides the best forecast. It depends on location and (I assume) what the solar forecast uses as weather predictions themselves
Perhaps there is experience with individual services. In my last project I used both forecasts and averaged them. The result was actually quite good, but I have no idea if it’s that easy with the Energy Panel . With Grafana it went quite well…
First, I tried Forecast Solar, but I cannot make it work. Many people helped me, but it’s just not working.
Then I changed to Solcast, it works and the forecast were quite close to the actual production, when the weather is relatively clear.
If the weather is cloudy, rainy, then it could depends on how often you update the forecast. Solcast free account gives you 10 updates per day. If you have 2 sites, it would consume 2 per update. So, not much 
I currently have 50 updates (old account) :).
However, I have both sides (west/east) in one and almost use the 50 requests.
You could still do this of course, I am half-way in setting up a forecast that ‘stays’ to compare tomorrows forecast with actual data (by then). You can use both API and then do the math to get to one…not too simple but possible. And as per HA_n00b three are limits to the free sensor but 10/d should be fine imo