IMO only...and I'm not trying to ruffle any feathers etc...but (again IMO)...AV software is nothing but a tax for the unaware (for lack of a more tactful word) user...
IMO...(1.) a solid (leak proof) firewall, (2.) a browser (like Firefox) with script blocking plugins and (3.)an awareness of URI's and message headers is all that is required for keeping a system free of malicious infections...
In 20+ years of browsing etc...the only virus I've ever had to deal with came from a game disk that was brought home from a high school...
For the most part a majority of malicious software (viruses, trojans, spy/mal-ware) are contracted via spam e-mail messages...The key to avoiding said messages/viruses etc...is to not be tricked into opening said messages...let alone clicking on links (regardless of how intriguing they may be) within said messages...
As for browsing...some of the worst sites for malicious, intrusive scripts are the social networking sites...
For instance...if a user has an open e-mail client and they log on to a site like facebook...one of the first thing a (facebook) script does is examines the associated address book and looks for email addresses that are already in their (facebook's) database...
Preventing scripts from executing through a browser is paramount to safe/secure browsing...
As a PHP/SQL programmer and backend developer for close to 20 years I learned a long time ago how powerful just the use of "cookies" can be...and how that power can be used for malicious purposes...
...folks that use browsers (regardless of flavor) right out of the box (lax security settings and no script blockers etc.) are just asking for trouble and for those users their only hope is AV software and that is OK as long as you don't mind the strangling effects that AV software imposes on most systems...
Again this is all just my opinion and experience not meant to rile AV software users...
Personally I recommend:
FireFox web browser with 'No script' and maybe 'Ghostery' as ad-ons/plugins
Comodo firewall
And learning to be knowledgeable/aware of bogus/spam e-mail message headers/attachments...