Which Mac OSX Antivirus?

While Macs are a lot less likely to get targetted by viruses there are still some viruses “in the wild” that target them.

So which antivirus software should I be using?

Which is the best?

Which is the worst?

Why is one better (or worse) than another?

I’m not concerned about costs, but I am concerned about functionality etc., ie. I don’t want some RAM hogging pile of junk that leaves my desktop completely unresponsive

Any / all suggestions welcome !