What is the best sounding Mahler symphony cycle?

Although I can't say who has produced the best cycle because there are so many variables I have to agree with @schubert  that every one of Fischer's efforts with the Budapest Orchestra is superb in sound and playing but there are many individual symphonies that I just couldn't let go. So for me the jury is out but I still love Fischer's efforts.

I very much like Boulez’s Mahler interpretations. I find them more intimate and less grand than my favorite conductors; eg, Bernstein, Abbado. It's a different take on Mahler.
The VPO recordings have the best SQ in the cycle probably due to the sonics of the wonderful Musikveiren and the recording techniques used.
Not quite audiophile, but worth having a listen.

I'll add to my previous comments that the Boulez  recordings are among the best in sound quality I have heard from DG. 

I would like to jump into this Mahler pool.
My favorite M, 5th sonically is Barbirolli on EMI.  Incredible detail yet warmth.
Another wonderful sounding 5th is the HDTT gold disc mastering of the 1963 RCA recording of Leinsdorf with the BSO.  I think Ivan Fischer's recording of the 3rd is sonically and musically superb.  Bernstein’s rendering of the 7th with the NY Phil sounds incredible to my ears and it’s my favorite interpretation.
A sleeper is Kiril Kondrashin’s performance of the 9th which I discovered many years ago on an Angel LP. It is now available from HDTT in a somewhat bright sounding but detailed recording. Again, my favorite version.  Other favorites sound-wise and interpretatively are Currentzis in the 6th, Szell and Maazel in the 4th and Solti in the 8th. I also admire the work of Roth.

I must admit I’m somewhat puzzled by the seeming preoccupation on this thread with the quality of the orchestras.  I would think it’s the interpretation that matters most.  When I’m listening to a pianist, I’m not overly concerned about the character of his instrument. Most of the orchestras discussed here are at or near world class.

In Russia, Richter recorded on some rickety pianos in the boondocks.  Yet, the genius shines through..