Which of the following traits is desirable in the presentation of a western pleasure horse?

The desirable trait in the presentation of a western pleasure horse is consistent and smooth movement. This characteristic is important because it reflects the horse's training, the rider’s control, and the overall harmony between horse and rider. In western pleasure, judges look for a horse that moves with a relaxed and fluid motion, showcasing even and steady gaits. This smoothness indicates that the horse is well-conditioned, comfortable, and exhibits an easygoing demeanor which is essential for this style of riding.

The other options, such as excessive energy and speed, frequent changes in pace, and frequent fidgeting, would detract from the ideal presentation. A horse that is overly energetic or fast may become difficult to control and would not demonstrate the calm and composed demeanor favored in western pleasure classes. Similarly, frequent changes in pace indicate inconsistency, which is not aligned with the smooth and steady performance that is judged positively. Lastly, frequent fidgeting can signify discomfort or lack of training, both of which would be seen negatively in a competition setting. The focus in western pleasure is on the horse's ability to maintain an elegant and unobtrusive style, making consistent and smooth movement the most desirable trait.