Laptop, running XP Home with Firefox (latest version), AVG (free edition; update check daily)(after using McAfee for 3 years I got fed up with the ever increasing CPU load this program poses), Windows Defender, Windows Updates (alert but I decide when to D/L and install; usually a day later to see if any trouble came up in the forums), Windows Firewall (after using McAfee Personal Firewall for 2 years). That should do it, for now.
I'm not gonna jump into *nix or Mac. *nix is what I work with at work, and I don't care for the user friendliness of it. Without delving deep into the ins and outs of any *nix, you're system is vulnerable for attacks. Plus, IMO WiFi still isn't implemented very well.
Mac is also no alternative. I don't like the prices for those pc's and laptops, I hate the lack of affordable software and I simply can't be bothered to learn yet another OS (after nearly every Windows version, DOS, OS/400, OS/390, Non-Stop Kernel, AIX and Sun). I know that learning a new OS after all this shouldn't pose much trouble but I'm tired of it. My laptop works the way I know and want straight out of the box, and that's exactly what I want it to do. In private I'm no longer a geek. 🙂