Own both, X2's are more comfortable for me but I don't have an abnormally "tall/long" head, I do tend to wear larger hat sizes (width/diameter). Both are comfy for me but there might be a problem with long skinny head shapes due to the limited vertical movement on the X2
Quick comparo
Sub-Bass - stronger on HP150 but also a little out of whack with the rest of the bass frequencies, significant bump around 30 hz, deepest sub bass is a little rolled off in the X2
Mid-Bass - stronger on the X2 but sounds natural, similar to what happens with speakers when they are put in a real livings pace (mild bass lift of 2-5 dbs)
Mids - X2 is hands down the winner here, there is a little upper mid recess on the HP150 that makes female vocalists sound "off" to me
HIghs - both fairly well extended, HP150's are more of an elevated plateau and the X2's have some spikes making them a little grainy.
Both are fairly easy to drive, I use my X2's for EVERYTHING and the HP150 for more sub-bass oriented music, EDM, Rap, etc. I also don't have a lot of closed headphones so the HP150's also come out when I need to prevent sound leakage.