So, a hint was given from the title but perhaps not what you would expect.
Which race fits best on a horse? I feel that orcs, draenei and taurens are way to big for most of them. While gnomes just looks like a… gnome on a big horse.
My personal preference has got to be human or bloodelf.
Let me know what you think!
Tall, slim races look the best, obviously.
Any female character model or as you said, elves and humans.
Are you hinting that Alliance should get more horse mounts?
Gnome is the correct answer here and I’ll show you why.
Horse:
Or a more advanced horse option:
And have you considered going bear? Pretty nice
Good luck friend and keep us updated!
Psst. Remember to always ride your mount bear chested. Trust me on this.
Haha not at all. But my orc female BARELY looks good on them horses my big bruddah
You completely discredited gnomes 
I guess it’s human. Other races not only look bad on the horse, but imagine, cow on the horse, doesn’t make any sense.
I think I love you. Increase gnome!
No point in arguing with these Gnome haters. They just don’t have our big brain capacity!
And they also lack our Gnome juicyness.
One day, the Gnomes (or cats) will rule the world. Trust me!
Bless you Dwarf! Your sweet comment has indeed increased my, Gnome-ness. 
Machagnome…
Me trying to hide my excitement whenever I spot a Mechagnome in retail:
yee-haa baby!!
Truth to be told, we were catfished in to that one 
When they said “mechagnome” we hoped/wanted the real McCoy, the mechagnomes of Keeper Mimiron seen in the Temple of Invention and Ulduar
And what we got? Those things you spot in retail… 
You and Tifa are hopeless. Hating on Gnomes, the true master race in wow.
Most people put yellow onion on their burgers. Clown puts red onion.
It’s sweeter and better. No debate
That would be the Vulpera, thank you
Try Sweet Onion… or White Onion
Sweet Onion then
are you trying to tame a mecha-horse?
No! You can’t control the clown, not even I can!
Trust me, I’ve tried.
I.Said.RED.ONION. And red onion it is. Thank you and have a good day ! 
I present to you…RED ONION!
I don’t want to controll you
Hides the collar and the whip
Just… proposed an alternative in the form of the Sweet Onnion, if you want… well… sweeter onnion in your burger
Red onions are subtly sweet and mild enough to eat raw. The vivid magenta color of their skin makes a great addition while sweet onions are larger than yellow onions, with a light skin. As the name suggests, sweet onions have sweet flavor due to a high sugar content, making them great for sauteing and caramelizing.
So you agree then. Good.
Red onion it is then
On this day, great progress we have made
Never disagreed
Red onnion is perfectly fine
Any kind of onnion are perfectly fine in a burger, even shallots and scallions
Sweet onnions just… sweeter than Reds 
Red onion is clearly the winner. Get with the program!