What class of amplifier has the most high definition sound ?

Georgehifi: Best, least coloured, fastest, cleanest, most dynamic a Class-A OTL tube amp, trouble is the speakers they love to drive are the "polar opposite" if full range 20hz-20khz.

+1 for the first part of that sentence.

I love my Atma-sphere MA1 amps. Clean OTL class A. I had the marvellous Krell FPB600 but have not looked back (much).

Speakers? You can get them. OTL amps can play the full frequency scale ok if the speakers are matched. And if the speakers aren't tuned to the amp, you can forget most of the discussion about amp quality, class A B or what.

For OTL you need easy to drive speakers, 8 ohm is marginal, speakers should be 12 ohm or more, OTL loves 16 ohm speakers with 90+ sensititvity. If not, your money on the OTL amps are wasted, you will get good but not excellent sound. 

I bought Audiokinesis Dream Maker speakers, and have been very happy with this combination.

What class of amplifier has the most high definition sound? 

The one that you want, but don't own. ;) 

Having built all manner of audio systems I assure you that the caliber of the system build has as much influence upon performance as the amp (or class of amp) itself. 

D_Schroeder wins #micdrop - BOOM!

@ vt4c
+1 Focusing on bias class is a waste of time. Find a good pairing with your speaker is more important. Difficult speakers will reduce the choice of amplifiers. 

(Except for this last sentence ... ¨ Shun those 85dB speakers.¨ in which I also believed until after years of owning a pair of passive ATC20s, decided to hook them up to a Mastersound parallel SET 20w/channel integrated and was pretty surprised. Speakers are 8 ohm nominal though and the Mastersound has some pretty hefty transformers.)

But getting back to OP,  comment by  georgehifi ...¨ Best, least coloured, fastest, cleanest, most dynamic a Class-A OTL tube amp, trouble is the speakers they love to drive are the "polar opposite" if full range 20hz-20khz.¨ ...seems to hold true with the  high efficiency speakers I´ve heard. For whatever reason lower efficient speakers have always appeared less colored.

Still miss my Celestion 600s (Stereophile measured them at 81db/1w/1mt. back in the day I believe), even with their lack of bass, but most definitely not my pair of Klipsch La Scalas which they replaced.

+1 @douglas_schroeder -- but the fact remains, when all other pieces of the audio system are dialed in and set, the amp choice still matters. As with everything in audio, the chain is only as strong as its weakest link. And you can carry that down to the design of the amp itself. No matter what class of amp, all the other design parameters and choices affect the final outcome. So while I might prefer the strengths of a Class A amp in general, I’ll take a well-designed Class AB amp over a poorly-executed Class A amp hands down.