Hi, I haven't used any Beyerdynamic headphones so I cannot comment, although I have read that the DT880 is very good (I don't know). I have used the Sennheiser HD600 but this has upper bass emphasis (drums and beats REALLY thump) and overall does not beat the HD250, in my opinion. My former HD600 did have an excellent neutral midrange though. My former AKG K550 also had great neutrality but lacked real, immersive sound dynamics, from what I remember hearing. If you're not listening to vinyl (i.e you listen to digital audio), I been given reason to believe that the Sennheiser HD800 performs very close to the HD250II. The HD800 is very expensive however and even though I'm quite confident that the HD800 would produce a superior stereo image to the HD250II, it may not actually be as musically enjoyable. I don't know as I haven't used the HD800...
There is only one device left that I've used that I like more than the HD250. It's still in production fortunately; Etymotic ER-4S, an In-Ear Monitor. This device offers very transparent, realistic sound. So far, there is nothing else in production that I've tried that I like more than the ER-4S.