I started writing this last week, but didn't get a chance to finish.
The question of comfort is relevant for two reasons. First, phones shouldn't be so tight as feel like clamps -- they'll produce headaches. This is also why on-ear phones are problematic, as they push down on the ears.
However, the other reason relates to acoustic sealing, and also implicates the specific type of phones. Acoustic leakage can and will be very annoying to other passengers. Accordingly, you want phones that seal well without causing pain. You also want closed-back phones, rather than open-back phones. As a rule, cheap phones (1) often are open-back, (2) have significant acoustic leakage, and (3) are not comfortable for long use. I've used a variety of phones over the years, but the most comfortable, the most effective at acoustic sealing, and the best at noise cancelling are the Bose QC line, though only th over ear, rather than on-ear, models. I routinely wear my Bose (currently the QC25) for the entire duration of a trans-pac flight -- as long as 16 hours -- without significant discomfort. They also have reasonable acoustic leakage characteristics, i.e. they won't disturb neighboring pax, and reasonably good sound quality. In my view, they represent the best compromise for active NC and audio on a plane.
I also have a set of Etymotics. I do sometimes use them on short flights (90 minutes or less), but they do get uncomfortable and their bass response is lacking compared to phones.