Frostwyrm... But since I don't have one:
It does look best under a blood elf, but my undead hunter has it too.
My druid doesn't use mounts at all because flightform>Everything.
I have a random mount macro active on most of my characters which rotates between some of my favorite mounts, currently for the undead hunter (who acts as my main at the moment, if only to collect mounts) and he currently has Sunreaver Dragonhawk, a few netherdrakes, green protodrake (yeah shortly after Cata came out I got my first protodrake ever) and Tyrael's Charger. Yes I do love dragons.
Mounts I'm missing but that I really want: Red Drake, Blue Drake, Black Drake, Sandstone Drake (Vial of sands), Frostwyrm, Green Drake (why isn't that in the game Blizz?) Twilight Drake, Blue Proto-drake, Quel-dorei steed (which my undead or troll can't get because they're Alliance-only for some annoying reason. All we get is another lame hawkstrider. There's only one cool hawkstrider and that is the Swift Red one, which is a lot easier to get since its only 5 champion seals and 500 g)