I fly Hawaii to Arizona and back several times a year, and the flights in coach sucks.
But I cannot justify paying for 1st class, and likely not for any upcoming SST either.
So I writhe for 6+ hours
Australia ... several times.
The discomfort varies greatly with the aircraft type. I really don't fit well in 787 seats. A380 was much less uncomfortable. 777 is not bad, either.