I am no expert by any length; but my preference will be:
#4 (the fallen horse) - while photographs are about beautiful composition, lighting, exposure, depth and so on, it is also about the subject. Photos of horses are plenty; rare to catch them in this unique position. This one stands out for the timing of the capture, though, artistically, it may not be the best photo.
#5 - focusing is just perfect in this photo. It has a blurred foreground and even more blurred background, with the horse being bang in the plane of focus. The expression of the horse, thru its eyes, are also captured well. Composition of the image is good; though perhaps in this picture it will have helped to have larger space around the horse, in violation of the rule of tight-cropping