I use Avira Free combined with Syagte Personal Firewall in xp and Comodo in win7 on my wife's laptop.
As for me i mostly never use windows. i use only Linux whenever i can. (the only drawback is games. you need windows for games such as NFS etc, others like quake etc runs on linux).
My personal Linux is Mandriva, started off with RedHat in ~2000, but later on switched to Mandrake (old name of mandriva)