Personally, I don't have any anti virus software installed.
There's no need for it if you use a multiple virus scanning website such as www.virustotal.com.
However, I would recommend that you experiment with different free (trusted) vendors.
Find which works best for you.
*** Beware of having multiple anti viruses installed at once, as they can "fight" each other for power, and cause the system to lock up. ***
I am partail to Mcafee. The site advisor, scan, and asking permission to do even offline changes. I have never had a virus propblem in the 3 years I have ran it.