For analog recordings the general rule is to find pressings from the home country of the label in question. The golden age for analog sound was late '50s to mid '60s. So for classical recordings from Decca or EMI get UK pressings, for RCA or Mercury get US pressings. For American jazz get US pressings (blue note, Prestige, Riverside et al). The earlier the pressing, the better the sound.
From the late '60s multi tracking became the norm, which changed the game with new engineering and production challenges. Some labels were more succesful than others in creating great sonics. Still, for British rock get UK pressings, for US rock, well you get the idea.
The most likely explanation is all record companies kept their original master tape and sent copy tapes to other countries. This quality step down at the source is elementary and can never be undone, no matter how good the engineering.
During many years of collecting vinyl records I've discovered that pressings which seem to be identical can differ greatly in sound. In some cases the matrix info on the deadwax with stamper codes and such can help explain these differences (the earlier the lacquer, mother and stamper, the better the sound). But many labels don't offer this kind of info, in which case comparative listening is your only option. This requires multiple copies (preferably in EX or NM condition), which is time consuming and costly.
This situation has created the business model of Better Records, who do all this work for you. I've never bought anything from them, but I'll bet their hot stampers are early copies from the country of origin.