Your favorite single ended headphone amps at differnt prices?

In this video:

from about 27:30 to 28:30 there is a quote from Jeff Wells from Wells Audio that got me thinking. What would the best single ended amps be in different price categories like:

Sub 250$, sub 500$, sub 1000$ and sub 2000$.

Which single ended amps are your favorites and what is your opinion on the quote about them from Jeff Wells, do you agree or disagree?