Like any Mahler, it is hard to recommend a best version, because there are so many interpretive standpoints you can take. So for instance I grew up on the old Haitink/Baker/King version, which is meant to be one of the peerless releases from the past, but I think it is matched by Tennstedt or more recently Boulez. My preference for less histrionic Mahler shows through in these choices I guess.
We went through a DLVDE phase in main Mahler thread several months ago and I definitely prefer the Klemperer/EMI among all the best known competition. The tenor part by Wunderlich really stands out as best I have heard and Ludwig's mezzo is among the very best, Klemperer has orchestral parts in perfect harmony with Mahler's vision for me.
I think MB was eventually converted to the Klemperer version as well......
Vocally I feel no one competes with Baker, but I'm more fond of Wunderlich than James King, and I'm very impressed with Klemperer's reading of the score. I don't really know. I guess ultimately I have to go with Baker and Haitink, but Klemperer's is a close second, and actually Oue with DeYoung is a very close third.
Haintink. I heard him do it live back in the late 80's or early 90's and it was so packed with emotion! I'll never forget it. Haintink is not known for his emotionally charged Mahler, but he really understands the full depth of this piece.