If the headphones have to be lugged around all the time the only benefits of the Grados would be their sensitivity. They would be able to play loud on any device you hook it up to. On the flip side you will go deaf because Grados are one of the most open headphones out there for letting ambient noise in. Also, if you are carrying Grados in a backpack, the cup design is also prone for letting debris like hair and dust to access the transducers. This causes what's known as "Grado Grattle". I have had it happen to me. Google, it is quite common.
The Beyer DT 880 and Senn HD 600 and 650 IMO are not headphones I would want to carry around with me all the time. They are too nice! I would be worried about ruining them. I would also be concerned with the Senns being driven properly and anything other than the 32 ohm version of the Beyers.
I also have the Audio Technica AD700 that John linked. Nice headphones at their price point, very comfortable, good sound but lack bass. However, they are WAY to big and bulky to be carrying around and you would look like a fool with them on in public.
As oldskool mentioned the Shure 840 would fit the bill very nicely. Their closed, good sensitivity, well balanced sound from top to bottom, they fold up and they are durable.
