A couple of weeks ago I bought a new pair of AKG K271 Mk II's for use with my iPod Touch amongst other things.
Initial impressions are very good indeed.
They will work plugged into the headphone socket of my iPod Touch but I think they will sound much better with a portable amplifier.
I've got a Meier-Audio HeadSix and I'm finding it to be really very good with these headphones.
I think you have to weigh up whether you want headphones or earphones yourself.
Those in ear earphones, the ones that go into the canal, do provide superb isolation but the reason I don't use them is that I like to be able to take my headphones off very quickly and I find pulling those out and then putting them back in again to be a bit cumbersome. A situation for me is that as I use trains a lot for travelling I want to be able to just whip my headphones off to hear announcements. With regular headphones this is very easy. Also when I'm buying coffee in the station or something I can so easily just take regular headphones off, have them resting around my neck.
I got the AKG K 271 Mk II's because I can easily make a cable for them and just plug it in. They come with two cables, one is too long for portable use and the other is a coiled one which is too bulky. However with the detachable cable using the mini-XLR connector it is very easy for me to make up a nice 1.2 metre cable to use for portable use.
I have found the isolation of the AKG K271 Mk II's to be very good indeed. This makes them perfect for train journeys. I hate turning music up to drown out background sound, so it is good to have this isolation. Also, I don't want to annoy others with their output.
The AKG K 271 Mk II's main disadvantage for use on the move is that they are not compact, not at all! These are full size headphones and it is surprising what a difference that makes, they will really fill up a bag when a compact pair of headphones will easily disappear into the same bag.
For "around the ear" headphones the AKG K 271 Mk II's ear pads are quite small. They do go around the ear but your ear will almost certainly be touching them all round. They are not totally clear of the ears like the huge K 702s. For me this is no problem but it is something to be aware of perhaps.
I'm finding the sound quality with the AKG K 271 Mk II's to be excellent. I got them because my K 702's have been such a success for me.