If you talk to people who compare the sound of every different release of various CDs trying to find the best (you’ll find them on the Steve Hoffman Music Forums), what matters is the the tape or the file used and the mastering.
CD releases from different countries released at the same time can be different, and CD releases from the same country released at different times can be different. For example, the 2012 American reissue of album XXXX may have used the original master tape while the 2014 Japanese reissue may have used a safety copy, or vice versa. And then there’s the mastering. Who did it? Was it a good example of his work, did he hit this one out of the park, or did the record label force him to compress it? And on and on...
Of course, the most popular albums have had the most releases or reissues and are more likely to have some good and some bad releases. Some albums only have bad releases.
Some people just love SHM CDs too. I think the packaging is usually better quality at least. Sometimes an SHM CD is one of the best sounding, sometimes not.
Anyway the Hoffman Forum is the place to learn about these things, but remember that the differences between CDs that are significant to some people there may not be as significant to you, and there may not be a consensus as to which release is the best.
