What class of amplifier has the most high definition sound ?

I would say it somewhat differently - tubes presenting harmonically correct soundscapes.

Only Class-A OTL's, anything with an output transformer is hamstrung.

Cheers George 

The question does hinge somewhat on what you intend to drive. A SET can measure great into a 16 ohm resistor. It would crap it's pants driving my Focal speakers though. 

I don't consider feedback a universal evil. Like anything else, it requires proper execution. 

Class D is out of the question, DOA, given it's gratuitous complex distortion at low power levels. Class A simply destroys class D at 1 watt where a huge amount of detail resides. 

what class of amp is the High Definition kind?

short answer? The High Dollar kind.

almost invariably greater fidelity goes hand in hand with more investment. despite ‘class’.

A, A/b, D, Hybrid, Tube amps which have an enormity of classes based on their output tubes, all have different levels of audio definition, or resolution. as the entry fees escalate in each camp, usually their resolution increases commensurately. there are over achievers and we all seek them out, but usually, more money means better most often. 

 the buyer beware note here is that it will take more than just an amp to realize the amps true abilities.

there needs be a great source, and of course, great speakers, or at least very competent ones.

a pair of Hiesenberg monos at $100K running into a pair of say, Joeseph Audio Pulsars isn’t gonna express the entire bandwidth as revelatory as they would with say, a pair of Legacy Aries.

amps are key, but so is the rest of the rig.

If there was a magic bean, don’t you think we would all have one?  Many choices, many tradeoffs and associated gear is among them.

The unstated inference is that anyone who agrees with what the magic bean happens to be, is dumb if they can afford it and don’t own it.

I found the match I like for my planars and understand others enjoy their amp for efficieny speakers.  There is no one size fits all “best”, no matter how much money you throw at the issue.  For those of us on a budget the choices are fairly proportional to the budget size and associated gear.

There are many great combinations at a variety of price points.  But alas, there is No magic bean.

I believe in Dilly Dilly.