I have 2 options to use for sound for game.

ALSA and OSS

Alsa and OSS both have 2 sub options:

Full Duplex and Use MMap.

Which Settings should I use for Best performance(not quality) For a Open GL game?

OSS is deprected in Linux, so most apps use ALSA. As to which provides best performance, I don't know. I use ALSA and it works fine on OpenGL games. I always change the sound settings to Full Duplex.

What I notice on the same hardware, in the same app (mpv) and with the same music file is the following.

When I play the mp3 320kbps files on mageia with ALSA + JACK the music sounds duller and less detailed. On FreeBSD with OSS4 in bitperfect mode and real-time sound settings the sound is significantly better although I find it hard to describe where the difference lies. I think there are several things that go a bit less than optimal when you use ALSA and JACK, and it's probably ALSA that's the problem because JACK on FreeBSD sounds fine. It's not just my impression, I did a test with a person and she thought the songs sounded better on FreeBSD.

I would like to ask if there are still distros that use OSS4 out-of-the-box instead of ALSA?
Are there any Linux distros where OSS4 can easily be used as the default sound API?