I recommend AIS, but I suggest that you try it before you buy it, as everyone has their own preferences. Its sandbox let's you isolate applications from your computer, so threats that are undetected won't be able to infect your system. The Silent Firewall is hassle-free, yet configurable. It also comes with a few network utilities (network lock, Geo IP/IP Tracker, fix network stack). The Antispam Filter is accurate and needs no configuration.