This is a hotly debated topic, and one that is sure to cause a few ruffled feathers!
We have found that the following GENERALLY works well and is partly the criterion we use in choosing our own dogs and puppies.
Firstly, the earlier the dog shows interest in sheep, we have found it is easier to train, and to create a good working sheepdog. It is much easier to work with an animal that shows initiative and interest than it is to try and coax an older animal into working.
Colouring and coat type has little or no influence on our decision. What we look for primarily are the following: Cooperation with the handler, early interest in herding (that is anything from geese to chickens to birds to sheep). In terms of physical build, we look for dogs with good strong and durable feet, and well-proportioned bodies. We look for dogs that easily and naturally form a bond with their handlers.
Another strong factor is stamina and good strong physical build. In our terrain dogs need to cover large distances without tiring too easily. We look for dogs with medium to long coats, as we have found that short hair dogs tend to have less resistance to extreme climates. As a last factor we favour dogs with slightly longer legs, this makes them more agile in rocky conditions.
We wish to emphasise that this is our personal preference, and that it may be best for you to decide on what the conditions are that the animal needs to live in, before deciding on an appropriate dog for your needs.