My longest flights ever were LAX-BNE or SYD-SFO on QF. Those clocked in at roughly 14 hours, IIRC, and were done in Y. I recall LAX-HKG, LHR-SIN, and LHR-BKK all clocking in at roughly the same time, as well. Considering I slept the majority of the time, I couldn't really tell the difference.

It's the 4-6 hour redeye flights that kill me, as they're too long to stay awake, but too short to get a full sleep.