In the world of horses, there is certainly a debate about reigning and dressage. They are actually similar in many ways, but generally, riders have a preference on which technique they choose to employ with their horse. While they are fundamentally different, so much of it boils down to the rider and the horse.
According to USDF, dressage if a French term meaning "training." It essentially focuses on developing the horse's natural athletic ability while also ensuring that the horse remains calm and has an eagerness to take direction from the rider.
In much the same way, reigning is similar. However, it focuses more on the working horse that needs the appropriate skills to work with livestock. According to USEF, competitions also exist for reigning horses where the rider shows off the precision and athletic ability.
Essentially, dressage and reining have many similarities, but perhaps the difference is found only in the goals of the rider. The Perfect Horse indicates that both types of riding can be a foundation for developing a strong bond between the horse and rider and each method can be used to teach the horse how to effectively move.
Check out the video to see the differences between the two. What do you think it comes down to? Is it really about the rider or the horse?