The best speaker you ever heard?

Casta D8 is my favorite. They don't sound like a pair of speakers to me tonality wise meaning I can't tell that the audio is coming from a woofer and a tweeter in a small sense or that it has artificial type sound like many other speakers do. Instead the D8's have a perfect realism that just sounds like perfect frequency response and pin point imaging floating in front of me. The dynamics in the audio are much better with these speakers at higher volume. When I listen to a big performance with many instruments these speakers remind me of how it would sound if I was at that live event. I find them very musical.

At the RMAF 2013 some of the most well received were:

Vapor Nimbus
Wilson Alexia
Focal Utopia
Sonus Faber Olympica
Magico S1 (really good on Hegel integrated)
SVS towers at 2k were the bargain performers of the show.

ACOUSTAT MODEL 3 UDL18 SUB POWERED/ GFA 565 ADCOM MONO BLOCKS

Sonus Faber Elipsa, all the better for being driven only by a McIntosh integrated, and a McIntosh CD player.
Former benchmark was the Vandersteen 5, with VTL amp & preamp & a Levinson player (Audio Concepts in Houston, RIP)
Recently heard the 2nd generation B&W 802 diamond with McIntosh 601 monos; very nice. Heard Cremonas in same room at same time, Diamonds very impressive.
My Thiel CS5's, connected to a Krell FPB 300 via Threshold FET 10 e & PS Audio Lambda, ain't too shabby, for a twenty year old system!
AudioAeros, at Audio Concepts, were very impressive as well, come to think of it...

Probably the most striking speakers that I've heard were the new "Pure" series PureVox speakers from BMC. While I sat there, they just picked them off the display; placed them on the floor in front of their other big speakers; hooked them up; and played them. Shockingly good sound even then, but after a day or two they were awesome.