I find the long-haul flights, especially from Los Angeles to Seoul, tough. I’m 177 cm tall, and am often uncomfortable on planes. Now that Amtrak has been taken over by a former airline CEO, on my last trip from LA Union Station down to San Diego, I discovered new seating arrangements, on a train, mind you, that left me no knee room. On a train!!
Anyway, Korean Air Lines (I work for a government university, who require me to fly either KAL or Asiana) flies A380s on the LAX-ICN route, and I’ve flown them probably a dozen times over the past three years. Not a bad ride, but still, at the end of the 13+ hours required for the west-ward flight, painful. Coming east is 9+ hours, much more bearable. To be honest, I have no comparison for planes on long flights — hopping around the US I usually take Southwest as their seats are comfortable even in “the full, upright position”. It’s a huge plane, feels massive on takeoff and even more so on landing, and waiting on the checked baggage takes a lot of time. I tend to sit in the furthest tail-ward section, as I can stand a stretch for a bit in the tail area.
By the way, I have a good friend, a nurse, in her 90s. She worked as flight crew, mostly on “the 5s” (https://en.wikipedia.org/wiki/Douglas_DC-5) doing the east coast to Europe with stops along the way — Labrador, etc. She also worked on the first double-decker passenger aircraft, the Boeing 377 (https://en.wikipedia.org/wiki/Boeing_377_Stratocruiser). She did not care for it.