Andrew
I was always a fan of semi-open back AKGs. First pair of k240 lasted me about 20+ years. Several years back, I upgraded to AKG K702. Very neutral, and as it was mentioned thin on bass. They are awesome for reference, and average listening is fantastic, however I found that mixing was not accurate, especially considering my very mediocre skills. Recording.... it's fun to record with these, as you can "hear" the room (and yourself), but the bleed is too much, especially with condenser mics.

Last year I decided to go with closed backs. Beyerdynamic dt 700 pro x. They are extremely nice set, but unlike open backs, closed back phones give me fatigue after about 30-40 minutes of use, but I believe (hope) my mixes improved. What I often do is keep both pairs close. Open backs composing & auditioning and closed back recording and mixing.

My advice to you, if/when picking a set, make sure you will be able to source parts like pads, headband, etc. For example, I have hard time of finding particular suspension parts for AKGs. Beyerdynamic on the other hand are known for sustainability / availability of components after the warranty is gone.

P.S. Not too long ago there was a thread here about headphone environment emulation apps. While it's obvious that mixing on speakers is a preferred method, it doesn't work for many... neighbors, kids, no studio space, cost of pro monitors, etc. While I was very skeptical about such "emulation" apps, I came to a conclusion very recently that it might be a magic pill for someone like me, who doesn't have the luxury of mixing on speakers. Check out Realphones 2. What it does, it corrects signal based on your headphones (they have settings for many models) and based on that gives you an idea of how your mix will sound...for example in real studio environment, bluetooth speaker, a car... many other "spaces". You don't bake your mix through it, but use it as a reference on master bus to adjust things and disable the plugin when bouncing tracks. You can get 41 day demo. I've tried it on my current project, so far I am impressed. I will use it for the next few weeks and if it holds, which I think it will, I will buy it when they run their next sale.