I've seen the Korean version, Taiwanese version, Chinese version latest Japanese version and the anime. It is the same story in all versions, but the Korean version of Kotoko (Oh Hye Ni) was more of a stalker than in the other versions. Don't worry. The Japanese version isn't that bad in that respect.
If we are going to judge which version has the lead as less of a stalker, I would list them as:
1. Say That You Love Me (Chinese version)
2. It Started With a Kiss and They Kiss Again (Taiwanese version and it's sequel)
3. Itazura na Kiss Love In Tokyo (Latest Japanese version)
4. Itazura na Kiss anime
5. Playful Kiss
Playful Kiss is actually my favorite. :P Followed by the Taiwanese versions. The version closest to the manga is the Taiwanese version. The one closest to the anime is the Japanese version. Also, imo, the one with the more authenic Irie is Playful Kiss. The character is very cold and emotionless, though, and so a lot of people didn't like that. The other drama versions have him toned down a lot so he is more likable.
I think the more authentic Kotoko is in ISWAK and TKA.
There is also an older Japanese version, but I have not seen it yet.
