TJ Combo for me. Such an outstanding build up at first before immediately hitting you square in the face with nostalgia. Satisfying.
Honorable mentions:
Orchid- Same as TJ Combo but since I have more memories of KI2/Gold than KI1, TJ wins
Hisako- I like the lullaby approach to the main theme. So soothing yet so sad. The crying in the background helps too.