I see Saturn games listed as M1 M2...Mn
What does it mean? Any link i can read? Thanks!
You mean 1M, 2M, etc.
it relates to the mastering code for the disc.
Here's an example of a Game disc where multiple pressings / masters exist
1M
http://redump.org/disc/3248/
2M
http://redump.org/disc/24292/
in most if not all cases the only difference is that the Audio tracks are shifted slightly differently (offset)
note how the hashes for the data track are identical.
I'm not sure what that is "mastering code".
Should i prefer 2M vs 1M or is there no difference from a player standpoint?
No ingame differences, it's just different copies of the game have audio data shifted differently. The ones with ingame differences are revisions (Rev A/Rev B/Rev C, etc.).