What is the best sounding Mahler symphony cycle?

MTT on SFSO (SACD) His 5th is excellent.
Abbado on EuroArts and Accentus (BluRay) #8 yet to come

Many (perhaps too many) excellent Mahler sets but you get to choose.

If you like Bernstein, "Mahler: The Complete Symphonies" box set has Lenny and the NYP at their best. It contains performances from the 1960s and has the most amazing remastering of any classical CD I've ever heard.
(DSD-remastered, 2008).

For a single 5th with good sound, try Abbado/Berlin Philharmonic (1993)

Abbado is one of the greatest interpreters of Mahler for sure. I don't know if his most recent recordings with the Lucerne Festival are available on CD, though, they might be just DVD.

Bernstein and Abbado are great Mahler conductors for sure, but the recordings are not really audiophile quality. I still like Abbado best of all on the first, Bernstein on the 2nd, Zinnman on the third, Solti on the 4th, Jansons on the 6th, Bernstein then Abbado on the 6th, Zinman again on the 7th, no favorite on the 8th or 9th, and Zinnman on the 10th. I have not heard any of the MTT recordings.

I can, unabashedly, say that I have heard most of these and find something appealing in almost all of them. However, the OP was asking for "audiophile quality" and, for me, that means a well-balanced and high resolution recording. This eliminates all the Bernsteins, unfortunately.

However, the Abbados on BluRay are superb in every way as are the MTTs and many others on SACD (Chailly, Boulez, Jansons, etc.) Zinman doesn't move me and the sound is only OK, imho.