ground mounts look better everyday.... their animations directly interact with the game world, flying mounts dont... as game worlds dont have simulated air currents or anything like that so its pretty much like flying in noclipmode in a game. :P
If WoW had simulated air currents and smoke when you fly, then i wouldnt mind flying at all, probably even prefer it... now its just... people justify flying because its more efficient.
(I love flying in Arma 3... its more efficient but its not as efficient as one would think... their biggest map, it still takes solid 20 minutes to fly across it in a helo, maybe 5 mins in a jet)