Fighting back can be a complex decision and greatly depends on various factors, including the specific situation you find yourself in. However, if considering the options you've provided, the most reasonable choice might be:
when your attacker is unarmed
This option carries the understanding that if the attacker is unarmed, there may be a higher chance of successfully defending yourself without escalating the situation to a more dangerous level. Always prioritize your safety and look for ways to escape rather than engaging in a fight if possible. It's also worth noting that every situation is unique, and personal assessment of the risks is crucial.