Big time fan of the Shenmue soundtrack here
If I think of my favorite tracks, they are almost always the ones involving exploration sessions or cutscenes in the night.
Daytime tracks are great as well but they were (on a general note) deliberately composed to convey the hustle of the working hours, think about Queen's Street. They usually have more percussive elements and faster tempo. Even in Guilin, if I remember correctly, although the day-tracks are really quiet, the night-tracks still manage to be even quieter and more atmospheric.
Hard to chose, but if I only have to pick one I'll have to choose Night-tracks .