In a horse-donkey, Donkey by all means.
And when it comes "down" to ponies, Minis are nice, ponies I never really liked them much, really.
Horses are more "classy" and donkeys are seen as more down to earth good only for work animals, but my experiences with them, I totally clicked more with them.
Donkeys might look less, but they are awesomely clever, thought as nails, and only slightly less stubborn than me, which is something good.