Chico helped point out mine, which were used near-mint.
IMO the Q isn't a one trick pony, I believe Mad used to have it listed as one of his top-5 all/rounders for a while before the X1 and MA900. And though the mids of the MA900 were nice (& well prominent in front of the treble and sub-bass), IMO that was more of a gaming-only headphone (like the AD700, but of a darker, kinda warmer character).
I dunno, I just haven't been " Done wrong" yet by an AKG.
I love the MA900 for music on the go. I mean it's smooth, it's musical. Not great for reference listening but great for casual one.
The K612 is more technically advanced and better suited for gaming imo but if your gear does not tame the treble sibilance well it's a very fatiguing headphone.
MA900 and K612 are two very different headphones and both have their place here. They get equal footing from me and obviously get different usage.