general advice is that nod32 is the best antivirus app, but the UI sucks hard. kaspersky is almost as good, with a reasonable UI.
but don't discount some of the other AV apps, especially if you want a value option (nod32 is very expensive compared to, say, f-secure, and not *that* much better)
and the free apps tend to work to varying degrees - but you may find yourself frustrated by the control they intentionally don't give you