In early childhood, it is better to use a collar rather than a sling. Because the dog's bones mature when he is young, all parts are relatively fragile. If you use a harness with too much force, your dog's bones will be damaged. Generally, it is better to use a collar tied around the neck.
It is better for adult dogs to use a harness. As adults, their bodies mature and their strength and movements increase. The collar type can easily cause the dog to exert too much force and cause neck problems. It is better to use a harness type.