Hifiman EF-2A gets a strong nod, according to
http://www.headphone.com/headphone-a...rating&dir=ASC .
An aside question I have regarding headphone amps. I was testing one out in a store, and tried something new out:
I set the headphone amp volume to max, and controlled the volume from the device itself - my iPhone.
The iPhone volume ended up around 1/2way up for comfortable listening, and the sound was spacious and open, with no hint of strain or distortion.
P.S.: I *did* remember to turn the amp volume back down after my audition!