The OP has set out a difficult question. So far the answers have focused on the labels which have excellent (amazing!) sound. The problem is what repertoire is best for the beginner. For example, the Ivan Fischer recordings of Mahler symphonies on Channel Classics and the Bach Japan Collegium recordings of the Bach Cantatas on BIS are both outstanding, but I would be hesitant to recommend them as the first classical music pieces to choose. And, unlike pop/rock music, almost all great classical pieces have many interpretations on different labels, so piece, interpretation and sonic quality all fit into the equation. Not an easy answer.
Larry