The ear cups on the M50x are smaller than those on something like the 380HD or the DT 770 Pro. Your ears could end up touching the the inside of the headphones which can be uncomfortable for some.
If you're looking for a headphone to keep you isolated on long plane rides, the M50x is probably not the right headphone for you. These headphones do not electronically limit exterior noises, it only blocks noise with its physical design.
The ATH-M50x are great sounding headphones with a sound that may fall in the neutral category, but with very slight boosts to the bass and highs; a slightly V-shaped sound. The bass is full and has a lot of power. The sub bass has a hint of elevation though, which can make the bass sound a bit loose on hip-hop or EDM tracks. The mids are fairly neutral with no elevation. The highs are also slightly elevated, which does not add harshness but instead gives the sound a shimmery and detailed feel.
This sound signature of the M50x makes it versatile. It is neutral enough for monitoring use, yet also has just the right qualities to make it a great choice for enjoying music.
The ATH M50x is made from high quality matte plastics which are quite resistant to damage without being too heavy. The hinges move smoothly and do not have unnecessary creaks.
The ear cups and pads are able to keep the sound in and block outside noise. These are suitable for a noisy office as even low volume music is enough to drown out those noisy office mates.
The ear cups can be folded into the headband, reducing its footprint. Combined with the carrying pouch and detachable cables, you can easily chuck these headphones into your bag when going out.
Audio-Technica finally updated the M50's built in cable to a detachable cable. The M50x even comes with three cables, a 1.2 m - 3.0 m coiled cable, a 3.0 m straight cable, and a 1.2 m straight cable. None of the cables have in-line controls though.
The bass is not overpowering. Instead, it is clean and controlled. The overall sound signature is focused on the bass but the mids and highs are in no way lacking either.
Depending on which model is purchased (16/80/250-ohm), your system may have trouble powering them to get a full sound and comfortable volume. 16/80-ohm should work fine in most systems. If not, you may need an external amplifier.
The DT770s are very comfortable to wear with its deep and spacious ear pads. The velour material used on these are smooth and breathable, and the thick foam provides ample cushioning. These headphones can be worn for long periods of time with no issues.
While the Sennheiser's have headbands which can be adjusted to easily fit a 'hatsize 62/63' head, the DT770 Pro and DT990 Pro headbands may need tweaking to make them work for larger heads.