Of course any answer to this question is going to be a generalization, but I’ve been in all three countries and have friends from all three countries so let me offer you my take:
Appearance – Japanese
Japanese girls usually wear makeup, a lot of them dye their hair, 60% ish don’t wear glasses. They dress in feminine outfits but are really quite varied. Example:
Japanese guys usually have long-ish wavy hair, a lot of them dye their hair, facial hair is acceptable. 60% ish don’t wear glasses. Again style is fashionable yet varied. Example:
Appearance – Koreans
Korean girls almost always wear makeup. 90% of them don’t wear glasses. A lot of them dye their hair. They dress in feminine outfits as well – but not quite as varied as Japanese. Their style is more cleaner and elegant. Short dresses and skirts are common. Example:
Korean men usually have medium length hair. A lot of them perm their hair. They don’t dye their hair as much as Japanese. 50% ish wear glasses. Style is focused on being clean and elegant just like the women and not that varied. Example:
Appearance – Chinese
Chinese women usually don’t wear makeup. They don’t dye their hair. 60% ish wear glasses. Their fashion is … very varied but I would say they have no cohesive style like Japanese or Koreans do. They seem to dress more casually in general. Example (actually this is really hard to find because just typing chinese fashion into google gives me lots of runway pictures rather than street pictures like for korean/japanese):
Chinese guys usually have much shorter hair than either Japanese or Koreans – alot of them like the ‘spiky’ look. They don’t dye their hair. 60% ish wear glasses (same as the women) and their fashion is varied and lacks cohesive style just like the women. I have to do some heavy searching again to find an example..
I think that it takes me so long to find good examples of Chinese fashion tells you they kind of lack the same focus on their industry that Japanese/Koreans have.
Personality – Japanese
Japanese are overly polite – so much so that you can’t really tell what they are thinking. They are totally indirect. They are very nice people but you can’t tell whether they truly mean it or not. They are the quietest and most reserved out of the three both for men and women. Japanese culture is all about strictness and manners.
Personality – Koreans
Koreans are the middle ground between Japanese and Chinese. Their manners and politeness level are in between; they will tell you directly if something bothers them or not but they won’t be overly rude about it. Korean culture emphasizes conformity more than anything – if you look or do anything strange it is very noticeable in Korea.
Personality – Chinese
Chinese are the most diverse out of the three. You have the loudest and rudest people out of the three, but of course that is not all Chinese. Chinese culture does not judge you as much as Korean/Japanese. If you do something that is rude or dress a weird way they most likely won’t care. They are the most open minded out of the three. But again this leads to Chinese people having by far the most variation amongst their manners and personality.
Hope that helps…