The best speaker you ever heard?

Overall best value/sound:
Vandersteen 2CE Sig II
Magnepan MMG
Magnepan 12

Favorite overall sound:
Current B&W 800 Diamond

Cost no object, sell the house/car to afford them:
Mcintosh XRT2K that had three 1kwatt amps per channel
I think the total cost of that rig was something like $250k?

Sound Lab A-1PX electrostatics. They sound real.

There are two.

1) Acoustat 1+1 & RTR ESR 15 disassembled, and arranged in a line source next to the Acoustat panels, with the Acoustat HF Transformer removed, which allows you to use natural roll off of Acoustats crossing over to RTRs. It also increases efficiency,and detail, by removing haze caused by HF transformer to equalize HF response. Combination give you coherence, and dynamics. Easily driven with HQ 30 watt triode wired tube amp. Best with Subwoofer, as the Sunlights but imaging, detail, and dynamics are superb, and tall line source does wonders for helping wall and ceiling reflections. They were the best I have heard, until:

2) Sunlight 308s. Simply amazing speakers. I am driving with a 2.5 watt 6a3 Triode single ended amp. Doc Gizmo got it right in his "Triode Guild" write up of these speakers. Acquired from Johnk who probably regrets letting them go. All of the positive aspects of the Tannoy's that people rave about on the Tannoy sites, but with no veiling,or the power requirements to drive them, as well as much more detail, and great imaging. HF is limited to 17k, so system also included a Fostex t90aex tweeter horn tweeter to 40k, and a pair of Audio Pro B2-50s for the bottom end.

Both speaker systems were/are the best I have heard, and I would be had pressed to choose between them, assuming I could recreate the Acoutat/RTR system. The advantage to the Sunlights is that a very high quality low powered tube amp is not as expensive to build as a very high quality high powered tube amp, but they are heavy, and bulky to move around. the problems with the Acoutat/RTRs are that they are electorstatic, with high voltages, and the power supply of the RTRs can be cranky, to say the least.

To put my answer in context, understand that I have been out of this game for the better part of 20 years, for reasons too complicated for this post. My "new" 2 1/2 (?) systems, accumulated over about 20 months, are soon to get the juice, however!

BEST: I think Mark Levinson's demo of master tapes on his HQD System at CES in Chicago about 33 or 34 years ago. That would be huge Hartley [sub]woofer units (15"-ers? Or was it 18"?)... stacked Quad "57" ESLs...and Decca (Kelly) ribbon [super]tweeters. Of course, the source may have had something to do with it... But, whew (!): "It's hi-fi, Jim... but not as we know it."

MOST MIND-ALTERING, JAW-DROPPING, FANTASMAGORICAL, and JUST PLAIN SCARY: Professor Hill's Plasmatronics ($10K a pair, and it seemed kind of outrageous!) at one of those same CES's. An ion plasma "tweeter" aboard, in case you don't know; and enough ozone to bleach the walls, I expect. Don't give me your quibbles about "integration"... The Roger Wagner Chorale, doing "Dry Bones", complete with Spike Jones-alike sound effects, could stop your heart... or scare the bejeezuz out of a corpse, and START ITS ticker! To this day, when some reviewer describes a ribbon tweeter as "lightning fast", I laugh.

Was probably a friend's KLH 9's driven by a Futterman OTL amp.
At one time, I owned the same equipment but they never sounded as "real" as my friend's set up. Very obviously room dimensions, speaker placement, absorbtion factors, etc. have much to do with what you hear and my experience certainly proved that to be the case.