Well, Jessica and Nicole are both right. :) It depends on what season you like and where you want to go. I personally love the colors of autumn and am even willing to put up with the crowds in places like Kyoto in November just to see the natural spectacle. But Kyushu in the winter is a great destination for people who don't like to be too cold but still want to see some amazing sights with very few visitors. There are fantastic seasonal festivals, tons of hot springs to choose from the winter in Kyushu promises comfortable hiking weather in places like Kagoshima. Really, it's hard to go wrong in Japan in any season. You just have to be honest about your own tolerance/preferences for things like weather and crowds.
The beautiful thing about Japan is you can experience many iconic wonders in each of its four seasons! So, it really depends on your preference of weather. For my friends and relatives from California, I usually recommend visiting during the springtime for Cherry Blossom Season (late Mar/early April) or in Autumn for the change in fall colors. The weather is usually comfortable during both seasons. Not too hot or too cold. Happy traveling!!
I agree with Jessica; however I personally also like the winter, especially in Tokyo. The weather is always nice, blue skies and a lot of sunshine; between Christmas and mid February you don't really need to worry about rain... (and mostly not about snow either). If you are planning to go to Hokkaido though, I recommend June - August/September. No real rainy season there and perfect temperatures (around 24 degrees Celsius).
I personally think Japan is good for 4 seasons. You can enjoy cherry blossom in Spring, water sports and lots of fireworks in Summer, falling leaves & onsen in Autumn and winter sports in Winter. But since the summer in Japan can be very hot and humid so some people might not feel too comfortable.
Summer can be uncomfortably hot and sticky in the cities, but personally it's my favourite time of the year, especially if you're visiting the countryside and looking to do outdoors activities such as hiking, biking, paragliding etc.
The Tohoku region is absolutely beautiful from mid-May onwards, after the long winter finally ends and the flowers and greenery start to come out. In Yamagata, my favourite month is June, as the rice fields have been flooded and the scenery is breathtaking.
Hiking is a great way to enjoy the natural beauty and escape the humidity, but bear in mind that many hiking trails deep in the mountains aren't accessible until at least July due to heavy snowfall.
Hi, my own opinion will be November. The top reason for me travelling in November for like at least 3 times is due to the cool weather (that's towards the end of autumn, lesser chance of rainy days), there isn't any school holidays (to avoid the crowd as much as possible), i'll get to see autumn leaves around at many places and lastly the highlight is the Christmas lightups at various shopping spots and even theme park all around Japan (For example: Seibu Yuuenchi, they set up big scale light ups from November till April of the following year, you get to enjoy some rides in there at night other than the illumination)
Either spring or autumn. Solely in terms of weather, it is without a doubt autumn, after the typhoon season has passed. The crushing humidity of summer is gone, and most days have clear blue skies.
And as anyone who has spent many years in Japan can attest, the autumn colors are every bit as beautiful as the cherry blossoms, and longer lasting too.