Avast but thinking of webroot
i currently use avast, but more for its features than its antivirus to be honest. i prefer its anti theft to any other, its the most feature packed anti theft i have seen so far.
however i do follow webroot on twitter and i must say it is very intresting, they post almost hourly about the latest exploits and ways of getting around security, to i am tempted, however i get Kaspersky free from my bank for my pc and its done me well, virus wise anyway, not so good against malware