If your talking about when you are just giving them a pet and a good scratch then it depends on the horse. I have found though that many horses love their chest and up their neck scratched. A good place to scratch a horse is at it's withers because that is a place they can't itch and it feels good.
Some horses love having you gently stroke their faces others hate it and will pull their head away.
It's really depends on the horse.
dog
green
pink
AFL
yes
telephone by lady gaga
Nando's!
Tacos.
pink cuz of Patrick
stalker >:D
Baby blue.
red and blue