None of them. I would say that the Japanese are having the best AI technology right now. US may be able to overtake them in the future, but I don't think that the Chinese will ever be able to compete with them. There is very little innovation in China.
I actually read on another
forum about the way Japan implements artificial intelligence. It appears to me that the way they are going to have their AI revolution is very well researched and they made sure that the people involved in creating a smart city based on AI are well aware of what is going to happen with their information.