What is the best sound system you ever heard?

In the old days ....a Decca cartridge (don't remember the arm or t/t), Audio Research electronics, and Infinity IRS speakers.

Here is a system I heard at a friend's house in 1978: Thorens TD125/Rabco SL8/Panasonic Strain Gauge cartridge, Marantz 7 preamp (used as a line stage), pair of Futterman H3AA OTL amps and a pair of Quad 57's. After hearing this I resolved to get a similar system!

Complete MBL system.  Radialstrahler 101, 9011 amp, 6010 pre-amp, VPI Aries. 

The Infinity IRS V speakers with $100,000 of associated PS Audio gear at PS Audio is a strong candidate for the best system I’ve ever heard. 

The one way up on Red Mountain Aspen CO, the one Dave Brubeck used for practice late 60s early 70s. All McIntosh everything. Some unknown monster midrange horn, time delay system, and concert grand piano of course. Also some kind of Joshua Light Show panels. I recall there was a big bunch of Ducati racing motorcycles in the garage.