It's one of the most important factors to me.
I'm considering Beyer DT-990's for both the comfort and the bargain price. AKG 701's have been ruled out of favor.
Edited by robertsong - 9/19/12 at 11:49am
I find my old ATH-A500 headphones to be the most comfortable I have ever worn. I literally could not feel them on my head after awhile. I think most closed Audio Technicas (A700, A900, A900x, W1000x, etc..) share a very similar design and will result in a similar comfort level. I tried their open counterpart in the form of an ATH-AD900 for a couple weeks. It was even lighter, but the driver touched my ears which made it less comfortable for me. So my vote goes to those closed Audio Technicas with the "wing" design or whatever they call it. The disclaimer of course being that I have only actually worn the A500, which is no longer with us. I am just assuming that the headphones with a similar design will have a similar level of comfort.
I'm assuming that with some AKG 240 velour pads and a bit of stretching the Superlux HD662 would be as comfortable as the AKG 240 since the designs are identical.
The panasonic rp htf600-s are pretty darn comfy too.