My dad gave me his old Bose AE for a few months before I got the M50. When I got the M50, it took a while for me to adjust to them comfort-wise, as the AE to me was extremely comfortable. The M50 headband put a bit too much pressure on the center of the top of my head at first, and the clamping force is significantly stronger than that of the Bose. After a week or two they will break in, but if you want to accelerate the break-in process you can stack a couple of textbooks or other large books vertically and stretch the M50 out over the books. Honestly though, the Bose AE and AE2 generally have gotten high marks for comfort. If you want a more comfortable headphone the M50 is not gonna be it, even after break-in. The beyerdynamic DT 770 PRO with its large, roomy earcups and soft velour pads is extremely comfortable, but it costs a lot more than the M50.
When it comes to sound quality, the M50 beats the AE hands down, especially if you're looking for a headphone suitable for audio recording. The M50 used to be known as a bassy headphone, but in 2011 audio-technica toned down the bass quantity. The revised M50s come in a white box and have a generally balanced frequency response, although there is a treble peak around 9kHz that can make cymbals and high-hats sound metallic and overemphasize the "S" sounds in vocals. The M50 is a closed-back headphone with shallow ear cups, so its soundstage is pretty narrow. Positioning and instrument separation are adequate. This is another area where the DT 770 PRO has a huge advantage.
The DT 770 PRO is a well-regarded alternative to the M50, but its price remains stubbornly high. The sound quality is good overall, though the bass is boosted compared to the M50 and not only does it have a treble peak, it also has a major dip in the upper mids/lower treble. Upper treble is rolled-off and the lower bass is slightly rolled-off, though it seems like it is significantly rolled off because the bass from 35 Hz and up is significantly above neutral. So why is the sound quality still good overall? The midrange is smooth and it's hard to get a better soundstage out of a closed headphone. So the DT 770 PRO wins on soundstage and comfort, while the M50 wins on frequency response and price. They are both built very well, although the DT 770 PRO has had a major issue with rattling earcups. My pair also had no bass on the right side, and beyerdynamic customer support was unable to fix either problem.
