Some qualities are easy to agree upon, for example, we want to see our dogs with dark brown eyes. Other qualities are much harder to agree on. Obviously, if the dog looks like a Borzoi the head is too long. And if it looks like a German Shepherd dog than the head is too broad. The area of disagreement falls in between.
Some people prefer a somewhat broader head with a shorter muzzle and more stop.
Others prefer a dog with a very long head with only slightly more width across the backskull as across the muzzle. These dog also tend to have a longer muzzle and less stop. In my breeding program, I will strive to produce dogs with moderate heads. This means that the backskull is clearly wider than the muzzle, but the line from the muzzle to the backskull should be smooth. I think this presents the prettiest expression in our Belgians.