Which Class D Amplifier? PS Audio, Ghent, Nord, Merrill or other???

Bel Canto. Best kept secret is the REF500M, while not as powerful as the 1000M, they are slightly sweeter with astonishing midrange, clean (but not sharp) high end and slam and drive.

Like I said, I think you can´t go wrong with Nord.
Hulgich Audio, an australian speaker company, won the Best Sound Award in a HiFi Show on 2017 in Australia and second place in 2018, using Nord One Up Mono Amps and competing with system costing hundreds of thousands.
I think for the price is a no brainer.

Lot's of good options. Test them all and get back to us! ;)

Although I haven't personally heard any premium class D amplifiers, I believe that GaN will be a key technology and market driver.

For those of you unaware of GaN (or would rather just listen than geek out!), here's my analogy ... Non GaN transistors aren't as fast as GaN so it's kind of like listening to MP3's at a lower versus higher bit rate.

Personally I believe this is a great development for HEA.  Without getting into the differences between amplifier classes, GaN (at least on paper) should more accurately reproduce wave forms and require less filtering and other processing. With faster transistors we should get better sounding (hopefully great sounding) amps that are cheaper, lighter and more efficient.  Maybe then the ear bud generation will learn to appreciate great sound and expand the market.

To be clear I believe that linear amplification with the proper components will always be better.

Personally I'm anxious to watch the market over the next 18 months.  If the big guys (Yamaha, Marantz ...) start buying/using GaN in greater volumes prices will drop.  This would enable the brands frequently noted here to focus on improving the processing mechanisms for even better sound.

For what it's worth.

Bel Canto Design REF600M and the Black EX.