I think it also depends on which direction you're flying home. If you're in Asia and flying East, a good J/F lie flat is more critical so you can be awake to "hit the ground running" when you get home. If you're returning from Europe it's going to be a daytime flight so assuming you can get to sleep when you get home in your bed and are not going from the airport to the office Y isn't as bad. If you're returning from any other destination that has red eye flights back to the US (South America, Israel, South Africa, etc) J/F is better.