I've had Beyerdynamic dt990pro for a long time and thought it'd be interesting to compare the two. Bare in mind that I've only had the AKG a week and they aren't fully warmed up yet, but my first impressions are obvious enough.
Where the AKG is worse is the soundstage. The BD have a wider field where the panning seems to be spread more. The AKGs sound closer to the head. The result is that the BD sound more 'light' while the AKG more closed in. I'd almost compare it to open and closed, but not in the sense of physically open and closed cups. The AKG bleed more as well.
However, the BD are considerably worse in the high mids and the lows. The sound is very nice but they seem to be too forgiving. The AKG however are more honest, but less of a joy to listen to. Listening to my mixes I definitely notice a trend of putting the snare too sharp or too high in volume, which i had to with the BD to let them cut through the mix, which was an endless source of frustration. With other music the high mids are on the edge, everything seems to be more present than the BD and if you make a mistake, the AKG will reveal the mistakes. I expected a little more bass in the AKG but i'll refrain from judgement till they've settled, at least there is enough low to make a good mix and hear the full spectrum. The highs are right where they should be, clear and sparkly.
When mixing you want to switch between headphones and monitors and they both have strenghts and weaknesses and having a combo that works is paramount. I feel now, i've at least resolved an issue by buying headphones that actually do their job as studioheadphones. Even if I'd rather use the BD for listening, I'd buy the AKG instead.
They are very light. It's very comfortably that way but it makes one wonder a bit about the buildquality, but hey, that might just be prejudicial, and isn't relevant to the sound.
