This is going to sound terrible, but I couldn't care less who the singers are. Golden voices of the past don't make a whit of difference to me. It's all about the pacing and sound - so I go for at least stereo recordings, and then who's on the podium. Nina listed some favorites, but I'd add Varviso and Mehta. Probably Maazel, too. His Trittico is pretty impressive as are the Ravel operas.