Two things:
1. We need more visual differences, but we don't need different speeds. As someone who collected mounts in WoW, it's kind of upsetting for me when the total mounts in the game numbers... what, 5? Maybe 6? I don't really count the different bardings, because I hate the bird and they won't go on my unicorn.
2. Right now mounts behave exactly like your character, but faster. What if, and just think about this for a moment, but what if mounts behaved more like individual entities? Think of Epona from the Legend of Zelda games. Yeah you have control over it, but it definitely gives some resistance. It feels like a horse. Even better, instead of the animal teleporting out of our asses, what if we called the Chocobo with a whistle, and it spawned just out of sight, then ran over to us? Then we could double-click to hop on, and off we go. W

Why am I the only person who ever seems to want that from MMO mounts?