I have 20' of chain on my anchor and windlass. More chain is usually better/recommended then going with less if you can. Chain will help your anchor to grab and will prevent the line from fraying on anything that may be on the bottom. If you anchor in anything other then a shallow river or bay, then more chain IMHO is not even an option, it should be required. In nasty seas or an emergency, you will be glad you had the extra chain to help you hold bottom. I would say 10' is a minimum. And if you anchor in anything over 75+ ft I would opt for more chain. Another alternative is heavier chain, but usually windlass's require a certain style and size chain so that it can be retrieved, you cannot just use any chain or line. I agree with ocnslr, always go with a slightly larger anchor then what is required for your size boat.