I've done lots of flights, ranging from 20 minutes (scariest!!!!) to 18 hours.
And in my opinion once you're past 4 hours it all merges and time kind of loses meaning. While you;re on the plane it feels like you always have been, and once you land you feel like it was only a second ago you got on, if that makes sense?
I much prefer an 8 or 9 hour flight to a 2, 3, or 4 though, as even a 2 hour flight I want to get up or do lots of things, but you the planes on short haul don;t allow for it.
At least on a trans-atlantic flight you have the time to unpack your bag and get your books and stuff all sorted for the flight, and the planes are bigger, so you can take a walk to the toilets far away, or go and stand at the back by a window to stretch your legs.
Can't really do that on small european planes, which i think makes them feel more of a drag as you're stuck in your seat.