1. The wyvern
The wyvern is the model from which Blizzard cribbed the horrifying older version of Tauren cat form, but it was already awful in its own right. Compared to gryphons, wyverns look...well...terrible. They have a host of much less impressive and realistic animations and just seem like they're a lower-resolution model overall. The run animation on the player mount version makes it obvious that the thing was never meant to run, and the top of its head looks like somebody took an experimental swing at it with a frying pan. I have yet to see a Horde player fly one of these monstrosities longer than they absolutely have to.
Dear God, someone please put this affront to nature out of its misery.