Only because I personally prefer over the ear designs, I'm inclined to give the nod to the HD 280's here. But not having a detachable cable is a deal breaker for me... which is why for travel I stick with my Sony MDR-NC60 which I will often use with no source attached at all.
For all the talk about sound quality, if I'm traveling on an airplane and using headphones, what I most want is noise cancellation and reasonable comfort -- which are not the points that everyone has chimed in about on this thread.
The on-ear design of the HD 25-1-II should lend itself well to spoken voice and audiobooks with only minimal reductions in noise isolation. I might suggests they'd ordinarily be overkill unless you wanted reference monitor performance. But they perform so well, I'd say make the investment in the HD 25-1-II.
Chances are that I won't even be using these to play music in that environment, and if I'm playing something it's likely to be an audio book where the frequency response is not so much of an issue. I might be using the headphones without any inputs. Opinions?