My buddy Mark asked me the what antivirus I'm using and that reminded me I haven't posted on this topic for a while. I've used a variety of these schemes. There was a day when Mac's didn't need antivirus, but that has long gone.
There's a huge variety of anti-virus packages and PC Magazine did a nice review of the "for pay" versions. The Bitdefender ended up on top. Also if you have Comcast, then you get the Symantec Norton for free, so that's a good choice if you have Comcast and want to get something out of it. It's complicated to get to. You have to login to Xfinity and then found their security. The other hard part is that the download is manual, so you can't script it.
This is one category where opinions really seem to vary. For instance, Mac World recommends the Sophos Home Protection if you want to pay and for free, the Avast Free Mac Security. I've used both and they both seem to work. The big advantage of the Avast is that it is not only free, but you can use Homebrew to do an automatic installation. That makes if very scriptable.