For Bruckner, I would go with Jochum's Dresden recordings. For me, no one else ever really consistently got Bruckner right. It is my opinion that no other composer's work suffers more from poor interpretation than Bruckner. I haven't heard enough of his DG recordings to comment, although I will say Bruckner's DG Te Deum is the one to have.
On Mahler, I suggest the DG recordings by Leonard Bernstein. He does some very interesting things, some of which I like and some I don't, but his interpretations are unique. His 2nd is particularly noteworthy, but I also like his 6th the best of any I have heard.
I have both the Barshai and the Jansons Shostakovich cycles. They are both very good. I would give the nod to Barshai if I had to pick one. The Jansons 4th is strikingly better than any other I have heard, and their is a breif recording of Jansons in rehearsal that makes for interesting listening.
On Mahler, I suggest the DG recordings by Leonard Bernstein. He does some very interesting things, some of which I like and some I don't, but his interpretations are unique. His 2nd is particularly noteworthy, but I also like his 6th the best of any I have heard.
I have both the Barshai and the Jansons Shostakovich cycles. They are both very good. I would give the nod to Barshai if I had to pick one. The Jansons 4th is strikingly better than any other I have heard, and their is a breif recording of Jansons in rehearsal that makes for interesting listening.