When shopping for a leash, you will find they are made of rope, chain, nylon, and leather. Different trainers prefer different materials. All of these materials are fine as long as you periodically check to ensure there is no evidence of wear or fraying. Here are some considerations when looking at the different materials:
Rope leads are vulnerable to chewing and fraying.
Some trainers recommend nylon because of its elasticity, and supposed comfort for the dog, however nylon can sometimes chafe or cut into the skin.
Many professional trainers recommend leather over nylon because leather softens and becomes more flexible with age, is easy to grip; yet it remains strong. However, some believe that dogs may be less likely to chew nylon, as opposed to leather.
Either a good quality nylon or leather will work well for most dogs.