I own the Audio Technica M50, Sennheiser HD 598, and Shure SRH 940, and all of these headphones are great in their own right and have their specific strengths and weaknesses, but as of late out of the three, the M50 has been getting more use, which I use in conjunction with my E7/E9 combo DAC/amp. Probably because of the more pronounced bass impact the M50 has, which goes along well with alot of the pop, electronic and dubstep I've been listening to lately. If I were to compare the three headphones, it would be something like this
Comfort - Sennheiser HD 598 (by FAR) > Audio Technica M50 > Shure SRH 940
Bass Impact - Audio Technica M50 > Sennheiser HD 598 > Shure SRH 940
Bass Detail and Extension - Shure SRH 940 > Sennheiser HD 598 > Audio Technica M50
Overall Detail/Resolution - Shure SRH 940 > Sennheiser HD 598 > Audio Technica M50
Highs/Treble - Shure SRH 940 > Sennheiser HD 598 > Audio Technica M50
Mids - Cant really say....
Soundstage - Sennheiser HD 598 > Shure SRH 940 > Audio Technica M50
Vocal Clarity - Shure SRH 940 > Sennheiser HD 598 > Audio Technica M50
btw, I think we can all agree that the Beats By Dre line of headphones sounds terrible with its mediocre mids and highs and bloated bass, and is overpriced, at least from the sound quality angle. Its just that Monster has better marketing and branding than the other high-end headphone manufacturers. They are stylish looking tho.