The Gaur is one of the best mounts for it's ability, in both PvE and PvP. Especially as a tank since you know when you're going to start the combat.
A 30% shield for your whole team + a 30% shield on top of that for yourself upon dismounting? Damn there's no stopping this one!
Fun Fact: The Gaur didn't exist on P2P until Eden brought it along with 13.0.