I'm being lazy, so I'm just going to copy (w/ some editing) a PM I sent to another member regarding my impression of K24P and K26P - which was pointed out to me to be in line with HeadRoom's impression (guess I'm not deaf after all, lol).
I really haven't done any real compairson between them, but for their intended purpose (i.e., portable) and sonics, I feel K26P is a much better choice, at least for me. K26P gives much better bass and I think it gives better balanced sound. K24P can be bit bright at times with some songs and the fact they're open phone does put a damper on things as far as portability is concerned (for me). K24P does pack better, though, since their pads are much thinner. But overall, I don't think it's worth having both of them, unless one wants a pair of good and affordable open headphones for portable usage. I just happen to have both since I bought K24P first (K26P were out of stock everywhere at the time).
Another thing I really like about K26P is that they are so much easier to get a good seal than PX200 that I've tried briefly, and you can also adjust where they sit on your ears a bit to get less/more bass if need be. Oh, and they're cheaper. Yeah, headband may be tricky for some, but I've found that by extending it completely before putting them on makes it much easier in this regard.