What is the best time of the year to arrive in Tokyo? Plan your Tokyo trip based on information about Japanese holidays, peak travel seasons, Japanese festivals and climate.
If this is not a business trip, and you can plan your time of arrival, I would say the decision should be based on 3 factors:

Tokyo's climate - What is the best month to visit Tokyo? Since at least two of Tokyo's seasons are very extreme, this is absolutely the first factor I would take into consideration. It just seems that if you're coming for a short visit- make the circumstances work in your favor as much as possible. Plan ahead, and choose the best time to come. After all - you do want to walk around in Tokyo's streets (which is the best way to absorb the atmosphere) and enjoy yourself.

Tokyo's festivals - if you have some control over the dates of your Tokyo trip do consider arriving at the time of one of the major Japanese festivals- cherry blossom (Sakura) , autumn (fall foliage). Tokyo's festivals are so unique and outstanding- the aesthetics, the costumes, the music, and the special dishes which accompany each celebration... it's a one of a kind experience, exceptional in every way.

Peak seasons of travel and Japanese holidays - certain times of the year can get very crowded on the public transportation system, museums, and Tokyo hotels. On the other hand, at certain Japanese holidays it is a custom for Tokyo people to visit their families in their home towns, so Tokyo actually becomes less crowded. In any case - if your date of arrival is close to any of these Japanese holidays, especially Sakura-the cherry blossom, or Tokyo school holidays-do book your Tokyo hotel in advance!

More on best time to arrive in Tokyo -
http://www.tokyo-top-guide.com/Best_Time.html

http://www.Tokyo-Top-Guide.com is an independent Tokyo site. Here you'll get the truth about Tokyo attractions - the real Tokyo information, unlike many official tourist or government websites, with their obvious interests. Written by a westerner-turned-Japanese.