Z-9/doc
In addition to being very fast like zombie dogs and other variants, it is fairly well armored making it relatively harder to damage than the others. That being said, it still has notably lack of health so a strong hit can get pass the armor and kill it.
Z-9's are often equiped with a Kevlar Dog Harness, hence the source of their armour stat. These can be disassembled, and provide the same number of Kevlar Plates as an MBR Vest. This makes them ideal targets for low to medium level characters looking to boost their stats through tailoring.