Pure guessing here – the top 3 is defenetly up there I am sure…
I have my doubts about casinochoice though. Also the value of a community like CM and WOL is really difficult to guess – are people just chatting or actually signing up and playing – who knows?? 
#1 gambling.com
#2 casino.com
#3 onlinecasinoconditions.com
#4 winneronline.com
#5 casinomeister.com // casinochoice.co.uk
I have only taken into account sites in english – I am sure there are many sites in other languages making a killing witout many people knowing about it.