I've used the AKG 240's quite a bit but now I'm using the Sennheiser HD650's. They fit better and I like their sonic qualities more than the AKG 240's. That said, all the mixes I've done using only the AKG's sound great on the HD650's. The reverse, not so much. On durability, the AKG ear pads typically age and crack. So if you go that direction, be prepared to replace the pads. Whichever headphone you choose to mix, make sure they they are open back. Not something closed like the Sony MDR7506.
As Massive Master said, it's generally better to mix on monitors. There are a million threads on this issue and I'm sure the basic arguments remain unchanged: your neighbors hate monitors but they provide better stereo imaging and a better sense of volume between competing tracks. On the other hand, headphones eliminate room influences which are THE most important factor in mixing decisions. In fact, if you room sucks, I would argue that you are better off using cans. In a well treated room and one that is verified by measurement, stick with monitors.
Of course, my take on this is somewhere in the middle. It's kind of a revisionist viewpoint. Both headphones and monitors should be used. Monitors for imaging, panning, volume, etc. and headphones for hearing cracks, plosives, editing errors, etc. I also use headphones for dialing in small reverb adjustments and other plugin changes that, for the life of me, I just can't hear on monitors.