Grain of salt: my opinion is obviously limited by my experience. I only talk about what I’ve auditioned in >100 hours of listening. I don’t double blind test gear and I cannot parse the audio nuance like an audiophile because my experience and audio memory with personal gear isn’t vast enough for comparisons. However, I do know what I like.
Talking just amps: I recently dropped $250 on a headphone amp that is really giving me joy at my workstation: The Cavalli CTH.The CTH does everything well. To my ears, it sounds like an early 70s megabuck system… in a good way. (It drives my Etymotic E4, HiFiMan HE560 or Sennheiser HD 580 Precision below the 10-oclock position!) Bang for the buck factor is high.
While traveling I like my HeadAmp Pico Power. One can find them new on the internet, in sales, for $250. My only complaint is I needed get cables for my HE560 because I didn’t want to use a 1/4" to 3.5mm adapter. This puppy sounds great, gets about 40 hours on it’s 9v batteries and stays reasonably portable. Oh, and it costs about 25% of what my Headroom cost.
I travel with only an Audioquest Dragonfly Black and ThinkSound ON2 (or Etymotic ER4) in my kit when I need to go light. (It takes the $199 ‘Red’ to drive my Sennheisers where I like) The $99 ‘Black’ sounds great on the ON2 and not bad at all with the Etymotic. Anyway, Dragonfly is a DAC/amp so it fails the apples and oranges test.