I would get a started young dog that has been working with a flock for a bit. SM are neat, and you could find a working example, but the resources to procure said dog would be high. A 6-12 month old Pyr pup from your neighbor Alpaca farm should do nicely. About both breeds, a lot would depend on the lines and the handling. Both can be independent and very capable guards. I feel the Pry would have the edge weather wise in your location.