This is what an Austrailian viewer over at IMDB had to say about "The Best Day Ever":

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The Best Day ever if I remember was basically an episode of the "best" moments of Arthur, well best moments for Arthur, Buster, Francine, Sue Ellen, Binky and Brain? I think. Sorry I can't remember the specific "best days ever" for the characters, Oh wait I remember Binkys was the episode where Binky and his family brought back their baby from China.

http://www.imdb.com/title/tt0169414/board/thread/208962729?d=208969517&p=1#208969517

Cool, a character clip show!