I personally don't consider the Mad Dogs a portable headphone, the alpha pads bring the center of gravity of the cup assembly too far away from your head. In other words, when you turn your head, inertia makes the cups "swing" out, it's not the greatest for moving around. The isolation isn't bad, but I just don't think they were designed to be used anywhere other than sitting down. The NADs can fold flat, which is nice for tucking them away into a backpack, but the headband shape makes them look a little weird on your head. They're also tiny compared to the Mad Dogs - but what "portable" doesn't?
Sonically, they're both great neutral headphones, with the Mad Dogs lying a bit on the darker side of neutral and the NADs on the warmer side. Technically, the Mad Dogs beat the NADs in terms of soundstage, treble extension, speed, and accuracy, although only slightly on the last two. The NADs have a slight mid accentuation ( "n" shaped, you could say, but very slight) and don't extend as high in the trebles, although goes as low as the MDs and hits a little bit harder. You can't go wrong with the sound of either one, IMO, so pick the one that you think better fits your usage needs.
Phew I'm glad we got that sorted out. :)
I still have a question for anyone that's heard both the Mad Dogs and the NAD HP-50. I'm torn between them. Ultimately I'm looking for something to replace my M100s as a portable / transportable can (with a more balanced sound). I know the Mad Dogs are pretty bulky to lug around, but I could live with that. Any thoughts would be welcome. :)
I used my Mad Dogs as portable/transportable, and I still use my Alpha Dogs at school all the time. I only partially agree with Ikarios. They are not an easy phone to do vigorous actions with, but they will stay on your head with simple walking. I rarely walk with headphones on my head though as not hearing anything bugs me (I will listen to IEMs with just one ear in if I have to). The only thing that really bugs me is that they do not fit around your neck very well with the cups being bigger than your average headphone. However carrying them around is not that difficult. I generally carry them by hand as I do not want books in my bag smashing them. I use the little pouch included with the headphones to protect them from scratches and what not (I would melt the draw strings together with a lighter as they come untied all the time, but do not melt them too much where they fall apart). I carry them around by hand from class to class with my water bottle, and I just do not find it that big of a deal. For a transportable headphone neither the Mad Dogs or Alpha Dogs size have bugged me.
The only thing I disliked is the sound coming out of most portable set ups. It generally takes a decent amp to power them. The only thing I have been truly content with that I have listened to is my DX100. Which drove both the MDs and ADs decently, not as good as a dedicated desktop Amp, but still within the range of being a very good sound. The Fiio E12 and Ipod combo was decent, but more of a bang for your buck set up over a very good sound (it would still best a lot of portable set ups imo).