- Bass = DT880 > HD600 >> K701
DT880 is most accurate in the bass to me. HD600 has plenty of it (for me), but more mid-bass which can sometimes exhibit a bit of bloom.
- Mid-range = HD600 > K701 > DT880
HD600 has most forward mid-range, but for me it is also most accurate and realistic. Instruments really sound like they do in real life - especially stringed instruments.
- Highs = DT880 > K701 > HD600
DT880 really are detail monsters - definitely brightest of the 3. Again - most realistic though would be HD600. At times DT880 can be a little too etched.
- Sound stage width = K701 > HD600/DT880
No question - K701 definitely wider with more separation. I really like them for classical and instrumental - but sometimes they suffer from not being totally realistic. DT880 and HD600 are about right IMO.
- Sound stage depth & imaging = HD600.
Hard to classify the K701 and DT880. The HD600 though is simply more holographic and gives more accurate spatial cues.
- Speed = DT880/K701 > HD600
Both DT880 and K701 seem to handle speed better than the HD600 - however for most of my music, speed is not a requisite so all of these cans are great.
- Comfort = DT880 >HD600/K701
DT880 in front but not by a lot. HD600 is very comfortable in it's own right - but I rank it with my K701 because they are lighter clamp + I have removed the bumps, and added a layer of very soft lambskin leather (with foam padding under it). My K701 are very comfortable after the mod.
Overall ranking - for me - HD600 = DT880 = K701
I know that's a cop-out, but I use all of them practically every day - just depends on what sort of mood I am in. They are each excellent headphones.
If you have some harsh recordings that won't stand up to a headphone with a high level of detail - maybe the DT880 may not be ideal. Their mid-range (while pretty well balanced) are not the focal point either - so consider that if vocals are important.
Parting observation - DT880 are far and away most detailed. HD600 are (for my ears) most realistic. K701 is somewhere in between - albeit with less than ideal bass.