Thank you for all your insights - gatefully received as Mahler is new territory so I didn't want to be deterred from Marhler by a bad interpretation. I must have heard chunks glancingly but not made a deliberate attempt to sit through a symphony. The DVD looks a good bet. I've been happy with what I've heard of Abbado and Bernstein so I'll choose between them. The Chicago recording is still around but it's a bit of a hope to get it by Christmas.
Cheers.
If that is new territory for you, you should definitely *not* get Bernstein (any of the 3, with the NYP, with the WP on video, and then again with the NYP). Bernstein was a great, great Mahler conductor but his priorities were not necessarily...balanced. He also has a lot to say about the 7th, but as a guide to this very complicated and sometimes puzzling symphony, especially for those who just begin to discover it, none of his recodings, as much as they are real musical trips, are good recommendations. You need a recording which lays out the material clearer and more balanced than Bernstein did. Just to listen to the music, the Boulez recording is actually quite good because it is so balanced. But, surprising as that is for Boulez, he doesn't connect all the dots nearly as convincingly as Barenboim or Abbado (at least in his CSO recording, like I said, I don't know the later ones), he just puts them all in the right places.
Besides, the last Bernstein recording (the one with NYP on DG) has reeeeeeeeeally bad sound. That's not even DG's fault - apparently Avery Fischer Hall really is acoustically nearly dead.