[andrewas]

A hardware firewall is superior to a software firewall as far as incoming attacks are concerned - with a good firewall, your PC becomes invisible to scanning and invulnerable to almost all attacks. It'll still fall if somebody with real skills decides they really want to get in, but thats rare.

However, a hardware firewall doesn't exist as far as outgoing traffic is concerned. If a malware does get into your system, theres no way the firewall can prevent the malware calling home with all your credit card details. Theres no way to distinguish that traffic from legitimate traffic. This is why you need both firewalls to be really secure, or at least you need a strong antivirus/anti malware so that the malware cannot install to the system in the first place.