In recent memory it has to the Kerr Acoustic K320 speakers. Nothing spectacular, but nothing obviously wrong - no sibilance, no bleaching, no cabinet issues. Eminently listenable fuss free sound through a Pioneer CD and smartphone streaming no matter what they were asked to play. Not sure about the amp, but it was a large black box with handles on the front.
I should also mention being stunned by the spooky imaging and scary dynamics of the Avantgarde Trios some 15 years ago. System featured a (ridiculously) deep plattered turntable with a, wait for it, £5k cartridge! Amps were some exotic valve types.
It was almost a time machine experience, but the trouble was the young chap demonstrating only played some 1950’s Jazz and didn’t seem keen on trying anything else. I still recall him telling us that it cost £5 in stylus wear every time he played a record.