I am now of the opinion that the Semyon Bychkov Das Lied is the greatest one ever recorded. It is available on the Waltraud Meier Documentary DVD "I Follow a Voice Within Me", but make no mistake, Das Lied is the main attraction here. Perhaps it has yet to be discovered by the Mahler community at large, because I have heard basically zero mention of it on the mahler-board, -list and review sites, which is why I am taking the time to draw attention to it.
If you have heard Bychkov's wonderful M3, this DLVDE should be self-recommending. Bychkov's style is reminiscent of Bernstein, but he's even better. It's a very theatrical, dramatic reading, but this is achieved with perfect tempi, perrfect pacing, really getting the pulse of each movement, as opposed to to unearned, momentary indulgences and tricks.
Bychkov leads both soloists to outdo themselves as well. Tenor Torsten Kerl reminds me of King from the Bernstein recording. And yet here we have a female soloist--surely the way this piece is best heard--of equal calibre to match.
Sound is ideal, very detailed, but not idiosyncratically so. Bychkov gets much of the credit for this as well.