Help choosing Beyer COP vs Ath M50

The great thing about the COPs is that the bass is adjustable, so you can get reference, flat bass out of these, or monstrous, head-thumping bass. I thought the COPs were slightly more comfortable. Bass on the COP definitely has more impact, but I'd venture that the M50s have better extension (hard to remember, honestly). Both are pretty detailed.

I've tried both and went with the ATH-M50. 

Sound quality:

This is always subjective (I listen to a lot of Progressive Rock) but IMHO I much preferred the ATH-M50.  I found the Custom One Pro's bass to be vague and boomy, and the mids to be much too recessed.  The bass on the ATH-M50 isn't always perfect and the mids are maybe slightly recessed but I found both to be superior to the COP.  The ATH-M50 has better treble response and detail retrieval. 

Construction:

The ATH-M50 clamps a bit harder but I suspect this will loosen up over time.   Also the ATH-M50 is more adjustable, twisting and turning every which way. 

The COP is of quality construction with metal harps and can be highly customized (if you're into that) but is no where near as adjustable as the ATH-M50.

The COP cable is thick, detachable and straight, about 5ft if I remember right.  The ATH-M50 cable is not detachable, is thick and is about 4ft long but has a sizable coiled section to make it expandable to about 9ft.  The plug of the ATH-M50 is made of metal, on the COP it's plastic.  Both headphones are well-made.

I really wanted to like the COP but for MY all-around needs (closed, portable/office, efficient, works well with many genre's), the ATH-M50 is an excellent value and is the clear winner.

From what i remembered M50 is more linear and COP is more fun sounding, I think COP suits your rock metal better