You don't need any 3rd party antivirus software to protect Mac OS X from malware. Macs are not immune to malware, but no true viruses exist in the wild that can run on Mac OS X, and there never have been any since it was released 10 years ago. The only malware in the wild that can affect Mac OS X is a handful of trojans, which can be easily avoided with some basic education, common sense and care in what software you install. Also, Mac OS X Snow Leopard and Lion have
anti-malware protection built in, further reducing the need for 3rd party antivirus apps.
If you insist on running 3rd party antivirus software:
- ClamXav is a good choice, since it isn't a resource hog, detects both Mac and Windows malware and doesn't run with elevated privileges. You can run scans when you choose, rather than leaving it running all the time, slowing your system.
- Sophos should be avoided, as it could actually increase your Mac's vulnerability, as described here and here... and here.
- iAntiVirus has an inaccurate malware definitions list that includes many items that aren't even malware, so their detection accuracy is untrustworthy. This post will give details.