If you like audiotechnica, get the AD900x instead of the AD700x, it has much more even mid and sub bass and more even treble.
There's also another popular headphone, the Sennheiser HD558. I have tested these headphones before and I will briefly explain my findings.
Clarity: AD900x wins for clarity, Sennheiser HD558 is a bit less clear and M50x is the least clear, not that it's not clear sounding, it just can't compete with open headphones in clarity.
Bass: Amount of bass is generally a preference with M50x having the most, HD558 being the middle ground and AD900x having the least. M50x has better sub bass though.
Soundstage width (how far sounds sound like to your left and right): Same as above, AD900x wins, HD558's is a bit smaller and M50x is the smallest.
Soundstage depth (how well a headphone can put sounds infront and behind you)
HD558 wins here with the AD900x and M50x being roughly the same.
Comfort: HD558 has deeper, oval shaped earpads that fit tall ears better and has the most padding, letting it win in comfort.
M50x and AD900x both touched my ears but that can be solved by stuffing cotton under the earpads to a degree.
Summary: AD900x is clearest, least bass, largest left/right soundstage
HD558 most comfortable with middle ground in clarity and bass, has deepest sound stage
M50x has more bass, best sub bass, is portable and blocks out some ambient sounds around you