BC and Wotlk were not so terrible with flying (BC especially, that gold sink + slow base flight was enough of a block that it didn't really matter).
Cata was pretty awful leveling-wise (just shuttling from one hub in a disconnected zone to another, try travelling around them with no flight). I barely went back to any of the zones except hyjal for molten front.
MoP's pros (beautiful zones and raids, flightless Isle of Thunder + Timeless Isle) cancelled out its cons.