I review a lot of headphones, and a number of them make my ears hurt. Not at first, but after 15 minutes or more some do because they put too much pressure on my ears -- and in the summer they make my ears sweat. Before we go any further, I have to admit predicting comfort about a given set of headphones is next to impossible, because ear and head sizes and shapes vary so much. One 'phone can't fit all heads equally well.
Even so, I wonder why so many full-size headphones have round or rectangular ear pads. Ears aren't round and don't have straight edges. I find oval ear pads fit better, though Koss' "D" shaped pads and some high-end Sennheiser pads more closely conform to the outer contours of the ear. I suppose styling too often dictates ear-pad design more than potential comfort.
Whatever the shape, I find too many headphones apply too much pressure against my ears and head. The pressure might not be all that bothersome at first, but after awhile my ears feel squished, and if I keep listening the pressure starts to hurt to the point I have to remove the headphones. I suppose headphone designers go for a tight fit so the 'phones are more likely to stay in place as you move around or dance, so maybe headphones with adjustable ear-pad pressure would make everyone happy.
In warm weather, my ears feel uncomfortably hot with some headphones. The "sweat effect" is more likely to happen with closed-back headphones; open-back headphones tend to have better air circulation, so they feel cooler.
Headphone weight is another consideration -- heavier ones tend to be less comfortable than lighter ones. I'd consider anything over 10 ounces (283 grams) on the hefty side for a full-size headphone.
I find some AKG and Sennheiser over-the-ear, open-back headphones to be the most comfortable I've tested, and Sony's MDR-1R and MDR Z7 are the most comfortable over-the-ear, closed-back headphones around. I can't cite any on-ear headphones as exceptionally comfortable. Still, take these recommendations with a grain of salt, headphone comfort is very much a personal taste issue.
Some users are uncomfortable with the pressure noise-cancelling headphones create as they block unwanted sound. I'm only slightly sensitive to the pressure, which is similar to the feeling I get when a plane is rapidly descending. If you're uncomfortable with noise-cancelling headphones, try a set of noise-isolating in-ear headphones, like the. They have ear tips designed to be deeply inserted into ear canals -- the tips work like earplugs and do a good job sealing out noise. There is a catch: some users find deep insertion in-ear headphones uncomfortable. Full-size, closed-back over-the-ear headphones are more comfortable, and can also block a good amount of noise.
Feel free to share your findings on headphone comfort in the Comments section below.