I don't know much about greyhound racing, but from what I've heard, they are cruel to the dogs.
I'm from Kentucky, so of course I enjoy horse racing. Some people say the horses are abused, but I don't find that to be true. The horses who race love their jobs. They are loved, respected, and treated very well. Horses are pulled from races if there's any sign of health issues. My only criticism is that the thoroughbreds are too young - they start racing at 2 years old, before their bones are fully fused, and that's why there are so many injuries.