r4 looks to me more softer, the korean version is more sharper in my eyes. Also i prefer the colour balance in korean rather than Madman version. To me Korean version wins out... (and I have it). The Korean version is a port of the japanese version I seem to recall.
R4 is identical to the R2uk and R2fr, ie a heavily contrast boosted, colour manipulated transfer that does not accurately reflect the proper look of the film - whereas the r2j, r3k and I believe the r3thai all do. All Kitano's films pre-Dolls suffer from similar problems on R4.
R3K and R3thai should both be ports of the R2J. I've got the R2J, Jompis has the Thai disc. I'm too lazy to do caps as I'm 99,9% sure they're identical to R3K. But if someone wants/needs them, then I'll do them.
I can confirm that the french release is like the R4.
Blurry picture, wrong colour scheme.
I used to be "the man who loves the movies you hate".
Now I'm just "that weird french guy with a cat avatar who comes to BnB once a year for no reason and then disappears again".