I would recommend it. I've used Macs since the 1990s and never previously bothered with anti-virus software. In the last year or so I decided it wouldn't do any harm to install ClamXav, based on user feedback here on MacRumors. It's a contribution to 'peace of mind', along with OSX's own safeguards, sensible Preference settings, maintaining a firewall etc, and staying alert for potential fraud, scams and the like.
Earlier this week I decided to run ClamXav to see if there was anything nasty lurking and I discovered I had a piece of junk e-mail that I hadn't trashed (or opened). ClamXav flagged it as an infected file. I suspect that it was aimed at Windows users, but I was delighted to see the results of ClamXav in action. (I don't run it all the time in the background but I do periodically inspect what's on my hard drive using it. Usually it comes up with a 'clean' result.)
I did try Sophos but after reading about it on this forum I uninstalled it.
For peace of mind ClamXav is a good tool to have at one's disposal, in my opinion.