Definitely Campercontact, I have been using their database for at least fifteen years and the very few inaccuracies found were in Scotland.
It includes both areas and campsites.
I have the free App but I seldom use it, usually I just do a simple search on their site, it includes three reviews which in 99% of cases is enough to understand if it is a good place or not.
As for the campsites, I use the Dutch Archiecampings which also has sections of members only Camper & Motorhome Club Certified Location and Camping & Caravanning Club Certified Sites.
Archie also has its own App .
Both have downloadable POIs for the most part of satnavs brands
Max.