Most people would advise you to use dried leaves. I've made it with fresh leaves before, and the salve works just as well, but fresh leaves can introduce moisture into the mix. If there's enough moisture, it can allow mold to grow or cause the oil to go rancid easier.

If you're only making a small amount you expect to use up quickly, fresh is probably OK. If you want it to be more stable for longer shelf life, go with dried. If you use a dehydrator to dry the leaves, use a fairly low temperature setting.