"Best" is subjective, but he has two good endings. One where he tells you more about himself and another where something else happens :).
To get his other ending try to get on his route, but don't score as many good choices with him. 1. Kai tells Subin that he didn't make any friends, 2. Kai doesn't joke in front of Xiuying, 3. Kai tells Intern Tang that he likes Moyu. This should work to get you on the 2nd ending.