Best city to visit in Japan in winter

between 20th November to 26th December??

Onsen :)

Uhh... do you like snow? Hate it? What kind of activities do you like to do? Eat? Are you staying there for a night? What kind of transportation are you using? Obviously there's a lot of subjectiveness when it comes to the "best city in Japan in winter".... a person who loves winter sports versus a person who loves castle towns will have very different opinions. Give us more information and we can help better.

i like snow and i am anime fans.I eat anything i want. xD

and i stay there over few night.

Assume that is next year given the date posted?
OK: 26th Nov: still good autumn leaf time: so start in Kyoto, then head to Tokyo, and if you like snow then off to Tohoku
http://www.japan-guide.com/list/e1102.html
and end in Sapporo.

i just stay in japan for 4-6 days only in 1 place.I not too sure which city is the best to stay during these time.(20 November to 25 December)

i just stay in japan for 4-6 days only in 1 place.I not too sure which city is the best to stay during these time.(20 November to 25 December)
OK: WHICH days? 20-25Nov OR 20-25 Dec, OR any 4-6 days between 20Nov and 25th Dec??? Very confusing.
If its snow you want, then go to the mountains, or north.
If its anime, then Tokyo and make advance reservation for Studio Ghibli.
If its November, then Kyoto, and go to the Koyo spots, esp the evening illuminations.
Essentially, do some reserach on this site about the offerings in the various places and decide from there.
Take into account your airport location, budget, and transport options.

4-6 days between 20 nov to 25 dec

Snow, anime and food for one place stay of 4-6 days in 20 Nov-25 Dec...

Then, definitely Tokyo. You can go to Gala Yuzawa, or north by Shinkansen as a day trip. Later in Dec is favorable, though.

Is there got any traffic jams because of a lot of people??

Japan has a lot of people. Period. Avoid rush hour.

And I like vocaloid too xD