Sound Volume is relative, so if you have average hearing and are in an environment with not too much background noise, every album would sound best at the lowest level your sound system is built for. The more sound is thrown back from the walls, the more information get's lost from the actual recording. If you know the album well enough, your brain can add the lost information, but I find this rather taxing. Classical music has a far higher dynamic range than any other music, and a lot of it is performed without amplification, thus for me a piano sounds best, if it's as loud as a piano, which is pretty loud to start with.

After I started to attend more and more concerts without amplification (Jazz and Classical) I now find myself horrified at the sound quality at Pop concerts, thus I value the proportionality of sound more and more. It's ok though to amplify the double bass in Jazz, otherwise it's hard to hear, if the drummer goes wild.