Go for isolation. I was impressed enough with noise canceling headphones that I ended up buying two different types some years ago. I was frustrated because I like listening to audio books and passing sounds (like a bus going by) would make me miss a phrase. I couldn't use them in the subway unless the volume was cranked all the way up.

A friend convinced me to invest in a set from Shure. Wow, what a difference! Because it blocks out all but the loudest noise, I can keep the volume to 4-5/10. As for comfort, I always found the in-ear type earphones marginally comfortable; I could only wear them for two or three hours without having to take them off. The Shures I can wear for all day - and have done just that while hiking. I've tried three different models and have been satisfied with each of them.