Most definitely during the school year, maybe February when there aren't any major holidays.( Like in October you can trick or treat). I went in May, though and it was not too busy, like during the Summer.
Christmas Day is considered to be the busiest holiday day at Disney theme parks. This is based on attendance at all Disney theme parks including Disneyland, Disney World, Epcot Center, Euro Disney, and all others.
Very crowded. It's one of the busiest times of the year.
The least busiest day of the week for shopping is typically Tuesday.
I heard from Disney mgr I used to work with that cosmic rays starlight lounge and Pecos Bills, both in magic kingdom at walt Disney world are the number 2 & 3 respectively busiest restaurants in the world behind the McDonalds in Moscow Russia. I can't find the exact source myself just yet but this ranking was from a couple years ago. I expect this hasn't changed as of yet. This would make them the two busiest in the U.S.
January
Aberdeen Airport has the world's busiest commercial helicopter operations.
amersham
The cities with the busiest airports in the world are typically Atlanta, Beijing, and Dubai.
the busiest port in the world is
The North Atlantic Ocean Route is the busiest trade route in the world.
Asia is the busiest continent in the world, both in terms of population and economic activity. It is home to more than half of the world's population and has some of the largest and busiest cities in the world, such as Tokyo, Shanghai, and Delhi.
The Port of Felixstowe is the busiest port in England, the 6th busiest in Europe and the 35th busiest in the world.