In my opinion, the best anti-virus software for Mac is none at all. There are no native Mac OS X viruses and, while it's not too good to be complacent, I can't imagine there being much of a target audience for it at the moment, not to mention the OS' already good security features.
I hate anti-virus software on Windows too - while I agree there is much more of a need for it on that platform, I've had as many problems WITH up-to-date anti-virus software on our newish Windows XP PC than before when we had none. The best solution, Windows-wise, I think is to revert to Windows 98. We had no anti-virus software on that system (used until a year ago) and no viruses either, although we may just have been lucky

. On the Mac, don't bother.
I hate to be cynical, but it wouldn't surprise me if the anti-virus software companies themselves were fuelling the virus and security issue. I mean, it is in their interest after all! The security market on Windows has become a massive business, and while, it's unfair to solely blame Microsoft for the problem, I find it sad that anti-virus and anti-spyware software has become accepted as one of the things you need for a PC.
As I keep saying, one of the major advantages of Macs is the whole no virus problem. Enjoy using a computer without all that crap slowing you down.
