Shenmue Dojo

Night, obviously. Why? The music seems much calmer and the atmosphere more lively.

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 .

The chillout and ambient vibe of S2's night is so nice.

Some of my favorites are:
Stand Qr. (Night) https://youtu.be/BCybsQGWwZ4
Lucky Charm Qr. (Night) https://youtu.be/7wY-yO-SXWo
Worker's Pier (Night) https://youtu.be/yC83aLg-efU
Fortune's Pier (Night) https://youtu.be/iMbwUZpPURo

mostly night but some day tunes are the best found in the game. especially white dynasty.

Night probably. Don't think anything tops South Carmain Qtr or Green Market Qtr at night.

This is tough to decide. I feel it's a bit unfair to rate all the tracks at once between day and night, instead of individual picks. There are just so many of them. Then again doing this on a quarter by quarter basis might be even thougher...

I can easily agree that the night tracks generally have a more calm feel to them and give off a stronger mood, with the exception of Beverly Hills Wharf, wich is just downright creepy. I still favor the music during the day however. When you play the game you hear those tracks much more than the night music so I'm simply more attached to them. They just give a greater feeling of familiarity. When I hear a day track of one of the quarters I can immediately picture the area in my head.

On a side note. It's just amazing what they did with the music for Shenmue II. Shenmue's FREE music is fantastic on it's own, with it's sometimes sweetly depressing feeling, depending on where you are in the story. But giving each area of the game not one but TWO music tracks that perfectly go along with the feeling of the place is one huge accomplishment.