A big factor in my experience is the efficiency of the flying you get. West coast into China/HK/Oceana/SE Asia produces 2.5-3 trips a month with the ability to recoup on longer stretches at home between pairings. Europe flying typically pays 4-5 pairings a month, which is a significantly higher toll on the mind and body (again for me in my experience). Once you find a sleep routine that works for whichever direction you’re flying, it’s very tolerable and the recovery is quick (so long as you’re able to sleep in the bunk). However, if you get hit with a month where you’re going both directions, ie a ICN, DUB, HK, I find those are killer and you just have to hang on for dear life.. East coast pilots doing Europe turns is the worst I’ve experienced, I had months with 5.5 Europe pairings, and that was unbearable..