The AKG K270s are the classic, big huge studio headphones.  There is little doubt if you see someone in these cans, they're tracking tasty licks on a new album.  Despite their size, they do tend to push in the mid-range frequency.  This might be by design in order to push them as vocal tracking headphones but if you just want to listen to music this is a minus.  On the plus side, these are 75 Ohms making driving them from even an iPod or portable music source no problem - something you will not do with the better sounding K240s.  These are sealed and from my experience they do a good job of isolating the playback track out of the recording microphones for most tracking, be it vocals or acoustic guitar.  The K240s will bleed somewhat if you're really pumping playback to the talent while tracking - these will virtually eliminate that.  If you want to track recordings and isolate the bleed from playback these will do nicely.