I think that the dt770 pro would be the best alternative, simply because they are excellent for games and movies. And they are soooooooo comfy, much better than the 250s for sure.
His taste in music (dnb, house, electro) is also good with the bassy bigboys that are dt770, albeit the ATs have much broader soundstage (oh horrible vocabulary, why do thee mock me), you are going to need a amp or something if you want to listen to anything but dnb\power metal with the dt770s
so imho:
toss out the 250's, I have\had them for a while(broken now) and they are not nearly as good as the dt770 in any circumstance
I think the dt770 would be best for you, but the M50 are not far behind, we all know the dt770 are ugly, they are ugly as ****, while the M50 are sexy beast.
The M50 works almost just as good without an amp as with an amp, but the dt770s do not (Except the 32 ohm version I guess)
altho, if you plan on never having it away from your computer, then you should most def buy the Dt770s, I see no reason to consider any of the other two
imho