I don't think there are very many "new" amps that are actually better than many of the older Krell Amps. Obviously there are some cost-no-object amps that may be, but not many.
Most of the newer amps are Class A/B or biased Class A-A/B, and then of course there are the Class D amps. Of course, there are also some straight Class B components, but those are not generally referenced as state of the art amps - more likely to be cheap components or AVR receivers not using Class D topology.
My amp is designed and built by a former Krell Amp designer (avoiding naming obvious names). I am seriously considering getting a Krell Amp of years ago that operates fully in Class A to replace my current amp.
I have owned Krell amps in the past and I found them to be absolutely wonderful amps. Got out of the hobby for about 10-15 years. Rejoined, and while maybe it's a bit of false memory, I just don't hear any notably improvements in amps today.
Sure, they may be more energy efficient, but I don't care about energy efficiency when it comes to my audio equipment. My washing machine was highly rated - turns out because it is very water efficient (hardly uses any water). Of course, it doesn't clean my clothes in a single cycle either, I often have to run it for 3 cycles to get the clothes clean, and unfolded if they were thrown into the washer folded. Does running for 3 cycles really save water? What about energy? I just ordered a new speed queen washing machine - I searched which washing machine uses the MOST water = speed queen. Then I googled which washing machines gets clothes the cleanest = speed queen. I have found that energy efficiency by design as a leading goal just does not deliver as good of a result - whether that's audio equipment, washing machines, lawnmowers, or even something as basic as a bathroom faucet (low water flow).
I tried some of the leading class D amps. None of them performed to my satisfaction level - YMMV.
