Hello from Finland :)
I was looking for a thread from the web just to get some reference how ppl compare these two headphones - found it - and now that I hava compared AKD Q 701 (my precious) and my friends new Beyerdynamic DT 880 Pro (250ohm) -headphones I must agree and disagree with certain comments presented here :)
First of all the DT 880's earpads are comfortable than AKG:s which feel a bit harsh after the DT's but AKG's pads are not uncomofortable but they are not silky either. If someone has auricles that are more apart - the beyers inner cushion might irritate auricles - i didn't have this problem. If you have extra sensitive skin, beyers would suit better for you. If you are just an "avarage person" you can easily listen to music several hours without any problems.
Someone said that DT 880 is neutral or the Q 701 is neutral - I dont think either is. DT880's problem is a round and bit soft sound - it also has a bit loundness-like problem with higher basses that akg really doesnt have.DT 880 is not actually very precise and it doesnt have enough texture. It makes the music homogenous: every drum stick's hit to the hi-hat sounds the same, you cannot here textures from vocals.
In the other hand Q 701 is much different. You here "everything". hits to the hi-hat differ, you can pick up the sounds of plektrum hitting the strings of guitar, but the sound is dry and it doesnt light up any emotions. AKG sounds like a reference headphone and that can get frustrating.
I listened to a variety of music from Chris Rea to electronic music - stuff from cd, turned to MP3 and also electronic (but good sounding) music ripped from vinyl (Rip: grado dj200i, sl-1200m3d, Xone:92, m-audio 2496).
The high's (escpecially hi-hat) is an interesting thing compared with these two. Yes, the hi-hat is stronger in DT880, but, it lacks the detail that Q701 has - that really is odd. I've been reading that DT 880 has a better highs, but i really disagree - they are more on the open but it doesnt give the same amount of data to the listener as Q 701 gives. It even (in some cases) is a bit disturbing, escpecially when the highs are in the surface (because of the mix).
The mids: I usually listen to the sound of vocals - Q 701 is way better. I really dont like when the mids are mixed up, but AKG really brings some clarity into the mids that DT 880 lacks. When listening to DT's there is always a feeling that the vocalist is standing behind a curtain - how thick of a curtain depends on the mix itself.
The Bass, ah, yes, the bass.. Q701 has a good bass even it lacks the power and mass. It goes deep and you can here it going deep because there is no disturbance at the upper bass section - tha bass doesnt "puff" all around and it totally lacks the upperbass sound (I dont know the word in English) but it sounds like you are in a barrel. DT880 has more mass and more powerfull lower section but again, it lacks details, nuances and textures (if one can say that about bass) and it has that barrelic sound sometimes.
How about the soundscape? DT880 is more like a headphone and Q701 is a bit more like listening to speakers. DT 880 didnt make me feel claustrofobic; you are not that inside the music - but in the other hand Q 701 isnt like you are listening to a stage concert either.
AKG Q 701 has more detail, less things that disturb, but a much more dryer sound that doesnt wake up any emotions. It is more reference headphone than a hi-fi headphone.
DT 880 is softer and more round, more bass and more highs, but it lacks nuances and textures. You cannot touch the surface of vocals, you dont feel the angle of the drum stick hitting the hihats, etc.
With AKG I like to listen to more acoustic stuff with variety of details and textures - but when listening to electronic music, house, etc, the DT 880 works better. It lacks the textures and has its cons but you can still enjoy the sound better.