I think the best April Fool is Google Analytics' Space Station April Fool.You should absolutely see this joke from Google.This is very creative and catchy April Fool. Lots of website builder did not understand anything including me.I do not know whether they do that every year or not, but they should do this kind of thing every year.You can reach the details here: 

http://makeusknow.com/categories/websites&internet/google-analytics-april-fool.html